Method and apparatus for modifying a video signal by back porch lowering

ABSTRACT

Enhancements to a video anticopying process that causes an abnormally low amplitude video signal to be recorded on an illegal copy. The enhancements in one version introduce into the overscan portion of the television picture, just prior to the horizontal or vertical sync signals but in active video, a negative going waveform that appears to the television receiver or videotape recorder to be a sync signal, thereby causing an early horizontal or vertical retrace. One version provides (in the right overscan portion of the picture), a checker pattern of alternating gray and black areas which causes the TV set on which the illegal copy is played to horizontally retrace earlier than normal in selected lines with a consequential horizontal shift of the picture information on those lines. This substantially degrades picture viewability. In another version a gray pattern at the bottom overscan portion of the picture causes vertical picture instability. In another version selected horizontal sync signals are narrowed, causing irregular vertical retraces. Also provided is apparatus for removing or attenuating these enhancements from the video signal, to allow copying.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] Enhancements to a video anticopy process, the enhancementscausing additional degradation to the picture quality when a copy of aprotected recording is played back, and additionally which reduce theviewability of unauthorized recordings of the protected recording.

[0003] 2. Description of the Prior Art

[0004] Video anticopy processes are well known. An example is Ryan, U.S.Pat. No. 4,631,603 issued Dec. 23, 1986, incorporated by reference whichdiscloses (see Abstract):

[0005] “A video signal is modified so that a television receiver willstill provide a normal color picture from the modified video signalwhile the video tape recording of the modified video signal producesgenerally unacceptable pictures. This invention relies on the fact thattypical videocassette recorder automatic gain control systems cannotdistinguish between the normal sync pulses (including equalizing orbroad pulses) of a conventional video signal and added pseudo-syncpulses. Pseudo-sync pulses are defined here as any other pulses whichextend down to normal sync tip level and which have a duration of atleast 0.5 microseconds. A plurality of such pseudo-sync pulses is addedto the conventional video signal during the vertical blanking interval,and each of said pseudo-sync pulses is followed by a positive pulse ofsuitable amplitude and duration. As a result, the automatic gain controlsystem in a videotape recorder will make a false measurement of videolevel which causes an improper recording of the video signal. The resultis unacceptable picture quality during playback.”

[0006] Column 2, beginning at line 5 states that the added pulse pairs(each pair being a negative-going pseudo-sync pulse followed by apositive-going “AGC” pulse) cause an automatic level (gain) controlcircuit in a videotape recorder to erroneously sense video signal leveland produce a gain correction that results in an unacceptable videotaperecording.

[0007] Therefore this prior art “basic anticopy process” causes anabnormally low amplitude video signal to be recorded when a copy isattempted. Some of the effects observed when the illegal copy isreplayed are horizontal tearing (positional displacement) and verticaldisplacement of the picture. Whether this occurs or not is often largelydependent on the picture content, i.e. presence of white (light) andblack (dark) areas in the picture. Therefore this prior art process,while generally providing excellent copy protection, with somecombinations of videotape recorders (such as VCRs) and television setsprovides a picture viewable by persons willing to tolerate a poorquality picture.

[0008] Also, with certain VCRs and TV sets the various well known priorart copy protection processes provide little picture degradation.Certain markets for prerecorded video material have a high rate ofpiracy, i.e. illegal copying of videotapes, in spite of copy protectionand these viewers apparently are relatively insensitive to the poorquality picture in illegal copies caused by the prior art copyprotection processes. Thus there is a need for copy protection processenhancements which degrade the quality of the picture even more thanthat of the prior art processes.

SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, the above-describedprior art “basic” copy protection process is enhanced by furthermodifying the video signal in several ways to ensure that the necessarypicture content requirement is met to maximize effectiveness of thebasic copy protection process.

[0010] The further modifications include blanking a portion of theactive video in the overscan area of the picture just prior to theoccurrence of the (1) horizontal or (2) vertical synchronization (sync)signals, and inserting into the blanked portion a waveform that (for avideo signal having reduced amplitude) is perceived by the TV receiveror videotape recorder as a sync signal, and so causes incorrectsynchronization of the VCR or TV receiver. Using this modificationespecially only on certain video lines or fields causes substantialpicture degradation of an unauthorized copy. Another modificationnarrows the horizontal sync pulses to cause sensing of a spuriousvertical sync signal in a TV set and will also affect certain videotaperecorders.

[0011] In the horizontal modification, the right edge of the picture isreplaced by a “checker” pattern appearing (like a checker board) ofblack and gray rectangles. The width of this checker pattern is chosento be within the overscan (not viewed) part of the picture whendisplayed on a standard television receiver. It will be understood thatwith an abnormally low signal amplitude, when the picture content islight (such as mid gray), the left edge of the black rectangle incertain video lines will trigger an early horizontal retrace as being anegative-going (towards blanking level) transition. When the picturecontent is dark, the right edge of the gray rectangle (adjacent to adark picture area), in certain video lines will trigger an early retraceon each line as also being a negative-going transition. (The descriptionof video waveforms herein follows the convention of positive amplitudebeing white and negative amplitude being black).

[0012] The horizontal modification checker pattern in one embodiment isgenerated at a rate slightly asynchronous to the video field repetitionrate, so that the checker pattern appears to slowly move up or down thepicture, at a rate of about 1 second for any given point to migrate fromthe bottom to the top of the picture or vice versa. The checker patternhas no effect on the picture when an original (authorized) cassette isreplayed since no signal conditions are present in the TV set which arein any way abnormal.

[0013] However, when an illegal (unauthorized or pirated) copy of thecassette is replayed using a videotape recorder, the signal attenuationresulting from the above-described prior art copy protection process, incombination with the checker pattern, causes the television sethorizontal retrace to occur early in each video line where either whenthe black or gray rectangle is present, depending on picture content andthe characteristics of the videotape recorder and TV set. The blackcheckers and gray checkers each may cause a transition of sufficientamplitude depending on the previous active video picture content. If thepicture content is light (white), the left edge of the black checkercauses a negative-going transition to black; if the picture content isdark, the right edge of the gray checker causes a negative-goingtransition from gray to the following dark area (typically blankinglevel). The difference between lines ending in black or gray in turncauses a horizontal displacement to the picture information, i.e. awiggle, which moves slowly up or down the picture.

[0014] The tendency of a television set to retrace (perform thehorizontal flyback early) is exploited by providing the light to darktransition (the left edge of the black checker or the right edge of thegray checker) prior to the location in the video line of the genuinehorizontal line synchronization (sync) signal. The early retrace sotriggered causes the picture information on the succeeding line to beadvanced, i.e. displaced horizontally to the right by an amount equal tothe distance between the negative transition and the location of theleading edge of the genuine horizontal sync signal. This displacementcauses a “tearing” (horizontal repositioning) of picture information.

[0015] A somewhat similar modification in the vertical picture senseinserts alternating dark and white bands in place of active video in thelast few lines of selected video fields in the lower overscan portion ofthe picture just prior to the vertical blanking interval, and/orextending into the first few lines of the vertical blanking interval.

[0016] This vertical rate modification is implemented in several ways.In one embodiment several of the active video lines (five or so)immediately prior to the vertical sync signal are made to alternatebetween blanking level and a gray level (typically about 30% of peakwhite) at a rate of about 1 to 5 cycles per second. This can cause drumservo unlock in the copying videotape recorder, or erroneous verticalretrace in the TV set, causing the picture from the unauthorized copy toexhibit vertical instability (jump up and down) at that particular rate,substantially degrading the quality of the image. In another version,two to five lines of alternating (modulated) white-black-white areinserted at the end of each or alternate video fields, with the sameresult of loss of vertical lock in a copying videotape recorder orviewing TV set due to interpretation of the inserted pattern as avertical sync signal when the video signal amplitude has been reducedthrough AGC response to a copy protection signal.

[0017] These vertical modifications in another version are both extendedinto the first few lines of the subsequent vertical blanking interval.

[0018] Addition of pulses to portions of the video signal after normalhorizontal or video synchronization pulses cause an abnormal videoretrace at this point, thereby being an effective enhancement to theprior art basic anticopy process. Typically these added post-verticalsynchronization pulses are at e.g. lines 22-24 of an NTSC televisionsignal.

[0019] Thus, the processes in accordance with the invention ensureoptimum conditions in terms of picture content for causing the maximumlevel of subjective degradation (1) to the replayed picture quality ofthe unauthorized copy and (2) to the recording and playback functions ofvideotape recorders.

[0020] The television set in response to the horizontal and verticalmodifications erroneously performs the horizontal or vertical retrace atan abnormal point. In the same way that a TV set will misinterpret thesignal, both the recording videotape recorder when the copy is made orthe playback videotape recorder when the copy is replayed can also beaffected. In this case it is the color circuitry of the videotaperecorder which is affected, with resultant picture degradationadditional to that caused by the basic anticopy process. This is anadditional effect to what has been described so far. This is because ofthe special way a videotape recorder processes the color information.The picture distortions include inaccurate color rendition andintermittent or permanent loss of color. The objective of themodifications thus is to further destroy the entertainment value of theillegal copy, over and above the degradation of the picture qualitycaused by the above-described basic prior art copy protection process.

[0021] The third modification to the video signal involves narrowinghorizontal sync pulses. In combination with a copy protected videosignal having reduced signal amplitude when re-recorded (copied), thisnarrowing causes the sensing of spurious vertical sync signals by avideotape recorder or TV set, causing vertical retrace to take place atother than the beginning of a field and so further degrading picturequality. This modification narrows the width (duration) of thehorizontal sync pulses on certain lines (such as lines 250-262) of thevideo field. These narrowed horizontal sync pulses, when combined with avideo signal that is of diminished amplitude, trigger a spuriousvertical retrace in many TV sets and videotape recorders, furtherdegrading the displayed picture. Narrowing the horizontal sync pulseswhere the checker patterns exist (lines 10-250) also enhances thechecker pattern distortion when an illegal copy is made.

[0022] It has been observed that the degradation of the picture qualityin accordance with the present invention is particularly useful wherethe prior art basic copy protection process provides relatively smalldegradation of picture quality or relatively small degradation ofvideotape recorder recording or playback. Thus the combination of theprior art process and the present processes severely reducesentertainment value of the illegal copy on a much larger combination ofvideotape recorders and TV receivers than does the basic prior artprocess by itself.

[0023] Provision of the horizontal checker pattern or verticalmodification only in the overscan portions of the television pictureensures that when the original recording or signal is viewed there is novisibility of the checker pattern or vertical modification, and indeedthe presence thereof is not known to the viewer of the originalrecording.

[0024] In other embodiments, the process user might trade off picturearea for effectiveness. (The user may elect to trade off visibility ofthe process when the “legal” recording is played, in order to enhancethe process anticopy effectiveness.) Thus, the modifications may inviolation of broadcast TV standards extend into the viewable portion ofthe video field, but still be acceptable in many applications.Furthermore, in another embodiment, the process trades off deviationsfrom accepted signal standards to further enhance the anticopyeffectiveness.

[0025] The modified signal in any case is displayed normally on any TVreceiver or monitor, providing the signal is of the correct amplitude.When the modified signal amplitude is reduced, as on an illegal copy,the conditions are optimized for the TV receiver to display or for avideotape recorder to playback a distorted picture. This will occur in aback-to-back video tape recorder copying situation using two videotaperecorders when the recording being (illegally) copied is provided withthe basic anticopy process of the above-referenced U.S. Pat. No.4,631,603.

[0026] The video signal modifications in accordance with the invention,in addition to causing lack of horizontal or vertical stability in a TVreceiver, also additionally have similar effects as described above on atypical videocassette (videotape) recorder, both during recording andplayback. VCRs use the leading edge of the horizontal sync pulse tocorrectly position the burst gate. If the burst gate is incorrectlypositioned, the color burst is not be sampled properly and loss of coloror distorted color results. The horizontal modification causesmisinterpretation of the position of the leading edge of horizontalsync. This will occur in the VCRs involved in both the recording andplayback of a (copy protected) copy, resulting in color loss/distortion.This effect can also be caused independently in the TV set. In the sameway that a TV set will tend to lose vertical lock as a result of thisprocess, so will a VCR. The result is a loss of drum servo lock in theVCR.

[0027] The modifications disclosed herein ensure that the requiredconditions for maximum picture disruption are always present, ratherthan relying on chance (the particular picture being displayed) thatthese conditions occur. Therefore the above processes which may includethe horizontal and/or vertical modifications and/or horizontal syncpulse narrowing have substantial value in enhancing the above-describedbasic prior art copy protection process, and more generally enhance anycopy protection process which reduces the amplitude of the video signalwhich is recorded when an unauthorized copy is attempted. Anotherembodiment to enhance horizontal jitter with illegal copying of videotapes is to use post horizontal pseudo sync pulses of approximately −20IRE amplitude (−40 IRE equals normal sync amplitude) and a width ofabout 1-2 μs varying in position in about a range of 1-2 μs after colorburst.

[0028] While the embodiments disclosed herein are in the context of theNTSC television standard, with modifications apparent to one of ordinaryskill in the art they are applicable to SECAM or PAL televisionstandard.

[0029] Also disclosed herein in accordance with the invention areseveral methods and apparatuses for removal or “defeat” of theabove-described video signal modifications, to permit unhampered copyingand viewing thereof. The defeat method and apparatus in one versionreplace or level shift the vertical and horizontal modification pulseswith a fixed level gray signal, and defeat the sync pulse narrowingmodification by sync widening or replacement.

[0030] In other versions, the defeat method uses added pre-horizontalsync pulses, post-horizontal sync pulses, or attenuation averaging. Alsodisclosed is a new method of defeating the prior art basic videoanticopying process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIGS. 1a and 1 b show respectively a normal picture and a modifiedpicture with the horizontal modification checker pattern and thelocation of the vertical modification;

[0032]FIGS. 2a and 2 b show a picture resulting from a video signal ofnormal amplitude, respectively without and with the checker pattern;

[0033]FIGS. 3a, 3 b and 3 c show the same pictures as displayedrespectively on a television set with a video signal of reducedamplitude, without and with the checker pattern and verticalmodification;

[0034]FIG. 4 shows a portion of a video signal with the checker pattern;

[0035]FIGS. 5a and 5 b show respectively a portion of a video signalwith the vertical modification not extending into the horizontal andvertical blanking interval and with the vertical modification extendinginto the vertical blanking interval;

[0036]FIG. 5c shows an additional vertical modification extending intothe horizontal blanking interval;

[0037]FIGS. 6a, 6 b, 6 c show a circuit for providing video signalmodifications in accordance with the invention;

[0038]FIGS. 7a, 7 b show waveforms illustrating operation of the circuitof FIGS. 6a, 6 b, 6 c;

[0039]FIG. 8 shows detail of flicker generator of FIG. 6b;

[0040]FIG. 9 shows another embodiment of a circuit for providing thevideo signal modifications;

[0041]FIG. 10 shows a prior art sync separator circuit;

[0042]FIGS. 11a to 11 o show video waveforms illustrating horizontalsync pulse narrowing;

[0043]FIG. 12a shows a block diagram of a circuit for horizontal syncpulse narrowing;

[0044]FIG. 12b shows waveforms illustrating operation of the circuit ofFIG. 12a;

[0045]FIGS. 13a, 13 b show in detail a circuit for horizontal sync pulsenarrowing;

[0046]FIGS. 14a, 14 b, show block diagrams of apparatuses for combiningsync pulse narrowing with the horizontal and vertical modifications;

[0047]FIG. 15 shows in block diagram form an apparatus for removal ofthe various video signal modifications;

[0048]FIGS. 16, 17, 18 show a circuit for removing the anticopy processenhancement signals via level shifting and horizontal sync replacement;

[0049]FIG. 19 shows a second circuit for removing the anticopy processenhancement signals via new sync and burst position replacement;

[0050]FIG. 20 shows a third circuit for removing the anticopy processenhancement signals via multiplying; and

[0051]FIGS. 21, 22, 23 show three additional circuits for removing theanticopy process enhancement signals via switching means;

[0052]FIGS. 24a, 24 b, 24 c show a circuit for nullifying theenhancement signals using sync widening;

[0053]FIGS. 25a to 25 h shows waveforms of the circuit of FIGS. 24a, 24b;

[0054]FIG. 26 shows another circuit for defeating the enhancementsignals via DC averaging and attenuation;

[0055]FIG. 27 shows an additional circuit of defeating the enhancementsignals via clipping;

[0056]FIG. 28 shows yet another circuit to defeat the enhancementsignals;

[0057]FIGS. 29a, 29 b show waveforms illustrating defeat of theenhancement signals via increasing sync amplitude;

[0058]FIG. 30 shows a circuit for defeat of the enhancement signals viaincreasing sync amplitude;

[0059]FIG. 31 shows another circuit for defeat of the enhancementsignals via tracking and holding circuits;

[0060]FIGS. 32a, 32 b show waveforms illustrating defeat of theenhancement signals via adding an AC signal;

[0061]FIG. 33 shows a circuit for connecting circuits for defeat of theenhancement signals;

[0062]FIGS. 34a, 34 b and 34 c show waveforms illustrating sync slicing;

[0063]FIGS. 35a, 35 b show waveforms illustrating the effect of widenedsync;

[0064]FIGS. 36a, 36 b show further sync slicing points;

[0065]FIG. 37 shows a circuit for enhancements of a checker patternusing post-sync pulses;

[0066]FIGS. 38a to 38 e show waveforms illustrating operation of thecircuit of FIG. 37;

[0067]FIG. 39a shows a circuit for defeat of the post-sync pulsesenhancement;

[0068]FIGS. 39b to 39 d show waveforms illustrating operation of thecircuit of FIG. 39a;

[0069]FIGS. 40a, 49 d, 40 g show circuits for defeat of post-pseudo syncpulses;

[0070]FIGS. 40b, 40 c, 40 e, 40 f, and 40 g show waveforms illustratingoperation of the circuits of FIGS. 40a, 40 d, 40 g;

[0071]FIG. 41a shows a circuit for defeat of post-pseudo sync pulses bypulse narrowing;

[0072]FIG. 41b shows a corresponding waveform illustrating operation ofthe circuit of FIG. 41a;

[0073]FIGS. 42a, 42 b show a circuit for defeat of the prior art basicanti-copy process;

[0074]FIGS. 43a to 43 g show waveforms illustrating operation of thecircuit of FIGS. 42a, 42 b.

DETAILED DESCRIPTION OF THE INVENTION

[0075] Horizontal Rate (Checker) Signal Modification

[0076]FIG. 1a shows a normal television picture 10, (without showing anyactual video information), i.e. including the left and right overscanportions 14, 16 and top and bottom overscan positions 7, 9. The part ofthe picture inside the dotted line 13 is the visible video 11.

[0077] The overscan portion of a television picture, as is well known,is that portion of the television picture not viewable on a standardtelevision set. Because of design limitations and aestheticconsiderations, standard TV sets are adjusted by the manufacturer todisplay somewhat less than 100% of the transmitted picture area. Theportions of the television image which are not normally viewable arecalled the overscan area. These portions are viewable on aprofessional-type video monitor with underscan capability. However, allstandard television receivers operate in an overscan mode, and hence theadded checker pattern and the modified lines at the end of each fieldwould not be viewable on such standard television receivers as sold inthe United States and elsewhere.

[0078]FIG. 1b shows the modified television picture 12 in accordancewith the certain modifications of the present invention, also includingthe overscan portions 14, 16. In the right-side overscan portion 16, achecker pattern 20 of alternating gray rectangles 24 and blackrectangles 26 is provided. This checker pattern information 24, 26provides the copy protection enhancement as described below. In thedisplay of the picture 12 on a standard TV set the checker pattern 20would not be seen since it is in overscan area 16. The vertical signalmodification is inserted in the bottom overscan area 9 and therefore isalso not visible.

[0079]FIG. 2a shows a video field 30, including the left and rightoverscan portions 32, 34, including in the active video 36 a verticaland horizontal picture element 38 (such as for instance a cross). Thisfield 30 is in accordance with the prior art and the checker pattern andvertical modification signal are clearly not included. This is alsowithout any reduction of signal amplitude, i.e. without provision of theprior art copy protection process.

[0080]FIG. 2b shows the field 30 with the addition of the checkerpattern 42 in overscan area 34 outside border 13 and the addition ofvertical modification pattern 87 to lower overscan portion 9. Sincethere is normal signal amplitude present, the checker pattern 42 and/orvertical pattern 87 have no effect on the appearance of the cross 38which is shown normally. It is to be understood that FIG. 2b is whatwould appear on a monitor showing the entire area and would not appearon a normal television receiver.

[0081] It is not possible to show a graphic representation of the effectof these signals on the VCR. A TV set will display artifacts due to theabnormally low signal amplitude; the VCRs used to record and replay thecopy can also be affected. In this instance, the servo systems of theVCRs will be disturbed, resulting in positionally unstable pictures.

[0082]FIG. 3a shows a picture 50 resulting from reduced signalamplitude, i.e. in accordance with the prior art copy protectionprocess, acting on a relatively insensitive VCR, but without theaddition of the checker pattern. This figure shows only the actualviewable portion (inside border 13 of FIGS. 2a, 2 b) of the picture on astandard television receiver. As can be seen, the cross 38 is displayednormally because in this case the picture content is such 'that there isno horizontal displacement. This is a case where the prior art copyprotection process provides inadequate copy protection, because thepicture is indeed viewable.

[0083]FIG. 3b shows the effect of the presence of the checker pattern 42of FIG. 2b when the reduced signal amplitude is present, i.e. when theprior art copy protection process is used in conjunction with thechecker pattern. Again in FIG. 3b the overscan portion is not shown.Here it can be seen that the cross 38 suffers from multiple horizontal“tears” 43 which occur at the location of the transition from graychecker 46 to black checker 44 (and vice versa) of the checker pattern42 of FIG. 2b. As shown in the enlarged view of FIG. 3c, portions 43 ofthe vertical part of cross 38 are horizontally displaced by an amountdependent on the distance between the left edge of the black portions 44of the checker pattern and the location of the true horizontal syncsignal in each line (not shown). Clearly, the picture 50 of FIG. 3b issubstantially degraded. The effect is further enhanced (not shown) bymoving the checker pattern 42 up or down slowly in the verticaldirection so that the horizontal displacements are seen to move, i.e.“wiggle”. This provides a virtually unviewable picture and hencesubstantial copy protection.

[0084] In accordance with the invention the checker pattern 42 of FIG.2b includes typically five black rectangles 44 each alternating with oneof the mid-gray rectangles 46. (Fewer such rectangles are shown in FIG.2b for clarity). It has been found that maximum picture degradationoccurs with approximately five gray to black transitions and five blackto gray transitions per picture height.

[0085] The signal level of the black rectangles 44 is set to be betweenblanking level and black level for NTSC (black level and blanking levelare the same for PAL or SECAM signals), and at black level for PAL andSECAM, and the amplitude of the mid-gray rectangles 46 is approximately30% of peak white level. The checker pattern 42 induces the zig-zag typepattern as shown in FIG. 3b; in other embodiments, there might be onlyone black rectangle 44 or two, three or four or more black rectangles 44per field 30 of FIG. 2b. Also the sizes (heights and widths) of theblack rectangles 44 need not be uniform.

[0086] The process causes early horizontal retrace in a low video signalamplitude environment by providing a negative-going transition, i.e.from the instantaneous picture level at the start point of the blackrectangles 44 to black level prior to the horizontal sync signals on atleast certain lines of the picture. The checker pattern 42 shown in FIG.2b is one such pattern which causes the intended effect.

[0087] The typical duration, (width) of the checker pattern 42 isapproximately 1.0 to 2.5 microseconds, as determined by the requirementthat the checker pattern normally is not introduced into the displayedportion of a standard television picture, i.e. is limited to theoverscan portion, and also does not infringe upon the normal horizontalblanking period.

[0088] In other embodiments, the horizontal sync pulse is narrowed andallowing the checker pattern to be wider. This would provide a greaterhorizontal displacement when the reduced amplitude video signal isdisplayed, but result in a nonstandard original video signal, whichhowever is acceptable for certain non-broadcast applications. Also, theparticular amplitudes of the mid-gray 46 and/or black rectangles 44 neednot be exactly as described above. Any effects resulting from thechanged relative position of leading edge of horizontal sync pulse andthe color burst can be corrected by a corresponding relocation and/orexpansion of the color burst.

[0089]FIG. 4 shows the horizontal blanking interval 60 for a singlevideo line, with a portion of the checker pattern present. Thehorizontal sync pulse 62 conventionally starts 1.5 microseconds afterthe start of the horizontal blanking interval 60. Active video 66, 68occurs both before and after the horizontal blanking interval 60.However, in accordance with the invention, a portion 70 of the activevideo 66 just prior to the horizontal blanking interval 60 has beenreplaced by either a mid-gray level signal 74 or by a black level signal76. (The gray level 74 and the black level 76 are both shown in FIG. 4only for purposes of illustration.) The loss of portion 70 of the activevideo 66 is not problematic, since as explained above in a standardtelevision receiver this portion of active video is not visible anyway,being in the overscan portion of the picture.

[0090] The transition 80 from the active video level 66 down to theblack level 76 appears to the television receiver to be a horizontalsync signal. This effect (as explained above) only occurs when the videosignal being displayed has reduced amplitude due to the copy protectionprocess.

[0091] The presence of the gray level 74 (the gray portions of thechecker) additionally ensures that the entire picture is not shifted tothe right. This would be the case if for instance there was a solidblack stripe down the right hand side of the picture. The alternatinggray and black levels provide the zig zag effect shown in FIG. 3b, whichhas been found to be intolerable for viewing by virtually anyindividual. Also shown in FIG. 4 is a conventional color burst 82 ridingon the back porch 84 of the horizontal blanking interval 60.

[0092] It will be appreciated from FIG. 4 that the only modification tothe video signal is the removal of the small portion of active video 70and the substitution therefore of either the gray level 74 or blacklevel 76.

[0093] The above described wiggle enhancement causes the checker patternto move slowly from the bottom to the top of the picture or vice versa.It is found that if this takes approximately one second for a giventransition to migrate from the bottom of the picture to the top of thepicture or vice versa, this causes optimum reduction of entertainmentvalue of the picture. This moving wiggle effect is provided by using afrequency of the square wave that generates the checker pattern beingslightly offset from the fifth harmonic of field rate, i.e. between 295Hz and 305 Hz, for NTSC television. The corresponding frequency for PALor SECAM systems is 245 to 255 Hz. This nonsynchronicity provides thedesired slow movement of in the checker pattern. As noted above, even ifsuch asynchronicity is not present and the checker pattern is static,there is still substantial benefit from the present process. Thefrequency of the signal generating the checker pattern can be adjustedto maximize the degradation of the picture quality when the lowamplitude signal is replayed and displayed. Frequencies between 180 and360 Hz for NTSC and 150 to 300 Hz for PAL (3 to 5 times the field rate)typically result in an optimum effect. The frequency may be varied withtime to ensure optimum effect on a variety of playback and viewingequipment.

[0094] In another embodiment, the checker pattern is located on thefront porch of the horizontal blanking interval, i.e. not replacing anyportion of active video. This somewhat reduces the amount of horizontaldisplacement; however, still there is at least some of the desiredeffect but resulting in a signal which retains all of the pictureinformation but does not conform to all NTSC standards.

[0095] The checker pattern need not be present on every field.

[0096] Vertical Rate Signal Modification

[0097] The above detailed description is directed to horizontal pictureinformation; the video signal modification and the consequent effect ofthis modification are in the horizontal picture direction. The relatedvertical rate modification described in the Summary is further describedhereinafter.

[0098] The vertical modification takes several forms. In one embodiment,groups of 1 to 4 lines in the lower overscan portion of a video fieldhave their active video replaced alternatively with white or black. Inanother embodiment, the last few video lines immediately prior to thevertical sync pulse are blanked, as are the first few lines of thefollowing vertical blanking interval, and the original picture video andvertical sync pulse therein are replaced with either a high level (suchas mid gray which is about 30% peak white, or actual peak white) or alow level (in the range of black down to blanking level) signal as shownat 87 in FIGS. 1b, 2 b and described above.

[0099] These vertical modifications are normally not visible to theviewer since the modified active video lines are restricted to thoselines falling in the overscan area 9 at the bottom of the picture ofFIG. 1b. (Also, the modified lines will be in a similar location to thehead switch point when video from a VCR is considered, and video onthese lines is unusable in any case as a result of disturbancesoccurring at and after the head switch point.)

[0100] In a standard NTSC video signal (or in other standards) as iswell known, the first three lines of the vertical blanking interval eachinclude two equalization pulses, and the following three lines eachinclude two “broad” vertical sync pulses. Normally vertical retracebegins shortly after the first of these vertical sync pulses.

[0101] The first vertical modification embodiment is shown in FIG. 5a.(Line numbers here refer to the second field of an NTSC video frame.)Lines 517, 518, 519 have their active video portions replaced with apeak white (1.0 volt nominal) signal; the same is done in lines 523,524, 525. In lines 520, 521, 522 the active video is replaced with ablack (0 volt nominal) signal. Instead of groups of three lines, thegroups may be 0 to 5 or more lines, and the white and black signals maybe modulated or switched in amplitude. Thus in the last several lines ofeach field the pattern of the white and black signals changesdynamically between fields.

[0102] The second vertical modification embodiment (FIG. 5b) blanks thelast two active video lines (lines 524 and 525 for instance) in a videofield and the first three lines (lines 1, 2, 3 for instance) of theimmediately following VBI. These two active lines are in the loweroverscan portion 9 (FIG. 16) of the TV picture. Then a mid gray (30% ofpeak white) video signal 87 is generated and inserted in these fiveblanked lines on a periodic basis. When the mid gray signal is not on(indicated by vertical arrows at lines 524, . . . , 3), these blankedlines “fool” the vertical sync circuitry of most TV receivers intoperforming the vertical retrace at the beginning of the first of thesefive lines, rather then normally five lines later at the beginning ofthe vertical sync pulses. Thus vertical retrace is advanced by fivelines. When these five lines are at mid gray, vertical retrace isinitiated at its proper location by normal vertical sync. It is to beunderstood that the number of such blanked lines and the amplitude ofthe inserted waveform may vary in other embodiments.

[0103] As shown in FIG. 5b, lines 4-6 (only 1-4 are shown) are as in astandard signal, as are lines 517 to 523. The modification is only tolines 524, 525, 1, 2 and 3; the active video portions of lines 524, 525and the corresponding portions of lines 1-3 are blanked (to black) orhave a mid gray signal at about 0.3 volts inserted. (It is to beunderstood that this amplitude is nominal, without consideration of theamplitude reduction effect of the associated prior art copy protectionprocess). FIG. 5 b shows a portion of a field with the mid-gray level.As stated above, the gray signal is switched on and off (“oscillates”)at a rate typically between 1 Hz and 10 Hz. In the version oscillatingat 1 Hz, there are 30 consecutive video fields with five lines havingactive video at blanking level, followed by 30 consecutive video fieldswith the five lines at 30% gray of FIG. 5b. As shown in FIG. 5b, thecolor burst in lines 524 to 3 may be blanked (or not).

[0104] This oscillation causes the picture to “jump” up and down by 5lines once per second (the oscillation rate) which has been found to beextremely irritating to the viewer as suggested at “x” in FIG. 3b. Thatis to say, on the fields where the vertical modification of FIG. 5b ispresent, the vertical retrace occurs early by five lines, followed bythe fields where the vertical retrace occurs normally. The earlyvertical retrace occurs because the overall video amplitude has beenreduced for instance to a maximum (peak white to sync tip) of 0.4 voltsfrom the NTSC standard 1.0 volts due to the presence of the prior artcopy protection signals. The vertical sync separator of the TV receiverthen perceives the first of the five blanked lines as being the firstvertical sync (broad) pulse and so retraces vertically shortlythereafter.

[0105] In another version of the vertical modification (not shown)instead of the last two lines of one field and the first three lines ofthe next field being modified as in FIG. 5b, the modification is whollyto the last five lines (lines 521, 522, 523, 524, 525) of active videoof one field; this avoids producing an “illegal” (non-standard) videosignal. A variation of this vertical modification is to relocate about 3lines or more like lines 524, 525, and in FIG. 5b to lines after thevertical sync area (i.e., lines 22-24). In some TV sets this causesextra jumping because the TV set “sees” two vertical sync pulses one atthe right time i.e., line 4 and one at about line 23.

[0106] It is to be understood that the vertical modification need notextend over the entire active video portion of a horizontal line. It hasbeen found that providing the modification over about ½ of the durationof active video in a line is sufficient to generate the prematurevertical retrace.

[0107] In yet another embodiment of the vertical modification (similarin most respects to that of FIG. 5a) as shown in FIG. 5c, the horizontalblanking interval is removed (blanked) on lines 517, 518, 519, 523, 524,525 where the white pulses are added. Therefore (like that of FIG. 5b)this is also an “illegal” (non-standard) video signal, but is acceptablefor many non-broadcast applications. The elimination of horizontalblanking on these lines increases AGC gain reduction (in VCR AGCcircuits). The white pulses on lines 517, 518, 519 and 523, 524, 525 maybe present in each field or modulated or switched in amplitude.Moreover, these lines with white pulses may change locations by a fewlines from field to field or some multiple of field rate as to inducevertical blurring effects when an illegal copy is made and viewed on aTV set. The groups of white pulses may extend over zero to four lines.

[0108] The vertical modifications to the video signal have no effectwhen applied to a TV monitor as a part of an original (authorized)signal. However, if the video signal amplitude is reduced sufficiently,for example by an anticopy process, the TV monitor will tend toincorrectly detect the vertical sync information, with verticalinstability resulting as described above.

[0109] Furthermore, if the vertically modified signal is applied to aVCR in conjunction with an anticopy process which results in a reducedamplitude video signal within the recording VCR, when a recording ismade the VCR's drum servo will tend to be disturbed. This is becauseVCR's typically require a “clean” vertical sync signal to maintaincorrect phase, and the presence of a jittering vertical sync signalcauses the VCR to lose lock. When the recording is replayed the visibleeffect is vertical instability of the picture plus intermittent noisebands which appear as the drum servo loses lock. (This is similar to avariable tracking error.)

[0110] In other words, the vertical rate waveform modifications functionsimilarly to the horizontal rate waveform modification described above,except that vertical disturbances are induced rather than horizontal.The two techniques combined are more effective in terms of picturequality degradation than either one on its own. Sweeping the pulse rateof the vertical waveforms increases effectiveness to more TV sets, i.e.,the frequency is varied between for instance 2 Hz and 10 Hz over aperiod of about 20 seconds. Sweeping the checker frequencies also willcause the horizontal tearing to go up and down resulting in a moreirritating picture when an illegal copy is made.

[0111] Apparatus for Vertical and Horizontal Modifications

[0112] Circuitry for inserting the above-described horizontal andvertical modifications is shown in block form in FIG. 6a.

[0113] The main video signal path includes an input clamp amplifier A1;a sync pulse narrowing circuit 96; a mixing point 98 at which thewaveform components of the horizontal checker and the verticalmodification (jitter inducing) waveforms are added; and an output linedriver amplifier A2. In this case also the video input signal into thecircuit of FIG. 6a may have the last 9 lines of each field blanked to areference level. U.S. Pat. No. 4,695,901 shows a switching circuit forblanking.

[0114] The process control and signal generation path includes a syncseparator 100; control circuit 102; circuits (see FIG. 6b) to generatethe required signal voltages which will be added to the main videosignal; and a switch selection system 104 (FIG. 6a) which applies therequired signal voltages under the control of the control circuit 102.(Note that in the drawings certain parts designations, e.g. U1, R1, OS1,A1 are on occasion repeated for certain components. These are notintended to represent the identical component unless explicitlyindicated.)

[0115] The input video is DC restored by the input video clamp amplifierA1. (Amplifier A1 is a commercially available part, for example theElantec EL2090.) Amplifier A1 ensures that the video signal (atblanking) is at a known pre-determined DC level before adding anyadditional waveform components to that video signal.

[0116] The resulting clamped video signal is applied to the mixing point98 with a source impedance Ro, typically greater than 1000 ohms. Theadded pulse signals to be injected are applied to the mixing point 98with a source impedance less than 50 ohms. When it is required to modifythe input video signal, for example with a checker component, theappropriate signal is selected and applied to the mixing point at a lowsource impedance, which overrides the input video signal from amplifierA1 and effectively replaces the input video signal with the requiredsignal. When the input signal is to remain unchanged, the switchelements 104 are all in the open state, with the result that the videosignal passes unchanged to the output line driver amplifier A2. Theresulting video signal at the mixing point 98 is applied to line driveramplifier A2 to provide standard output signal level and outputimpedance. An output of the video clamp amplifier A1 is applied to thesync separator 100 (this is a commonly available part, for example theNational Semiconductor LM 1881.) Sync separator 100 provides thecomposite sync pulses and frame identification signal required by theprocess control circuit 102.

[0117] The process control circuit 102 generate the control signals toturn on the signal selection switches 104 at the precise time (and forthe required duration) that the various signals are to replace the inputvideo signal.

[0118] All of the various signals which are to replace the original(input) video consist of a high or low steady state DC signal level. Forexample the checker signal “high” is a mid-gray level, typically ofabout 30% of peak white; the checker signal “low” is black level orblanking level. These various signal levels are generated (see FIG. 6b)from potentiometers VR1, VR2, VR3, VR4 which provide adjustable signallevels (or alternatively from voltage divider resistors for fixed presetsignal levels) connected across appropriate supply voltage lines. Thissignal is applied to the appropriate selection switch elementsrespectively 104-1, 104-2, 104-3, 104-4 via unity gain operationalamplifiers A5 to ensure the required low output impedance into themixing point 98.

[0119] The control circuit 102 generates the appropriate switchselection control pulses for the checker pattern and verticalmodification signals (see FIG. 6a). Checker pulses are applied only toselected lines; one example is to start the checker pattern at the 10thline containing picture information (i.e. after the end of verticalblanking) and end it 10 lines before the last line containing pictureinformation (i.e. 10 lines before the start of the succeeding verticalblanking interval). Similarly, the vertical jitter modification signalsare be applied only to selected lines, for example the last nine linesprior to the vertical blanking interval. Hence, both the checker patternand vertical modification signals require control signals with bothhorizontal and vertical rate components.

[0120] The video input signal “video in” (see FIG. 6c showing detail ofFIG. 6a) is buffered by amplifier A3 and coupled to sync separator viacoupling capacitor C1 and a low-pass filter including resistor R1 andcapacitor C2. Sync separator 100 provides composite sync pulses andframe identification square wave signals. The composite sync pulses areapplied to a phase-locked loop (PLL) 110. The phase control (“phaseadj.”) of PLL 110 using potentiometer VR₆ is adjusted so that thehorizontal rate output pulse starts at the required start point of thechecker, typically 2 μs before the start of horizontal blanking (FIG.7a). The output signal of PLL 110 is used to derive the horizontal ratecomponent f_(H) of both the checker and vertical modification signals.The burst gate output signal of sync separator 100 is inverted byinverter U5 which provides a clamping pulse for clamp amplifier A1 (partnumber EL2090).

[0121] The frame identification square wave output (“frame pulse”) ofsync separator 100 is applied to a one-shot circuit OS1 to provide aframe identification pulse of approximately 1 μs duration. This one-shotoutput signal f_(v) is used to derive the vertical rate component ofboth the checker and vertical modification signals. The horizontal-ratephase-locked loop component f_(H) from PLL 110 is applied to the clockinput terminal of a memory-address counter 114. The frame(vertical)-rate one-shot output signal f_(v) is applied to the resetinput terminal RS of counter 114. The memory address counter 114 outputsignals are applied to the memory 116, typically an EPROM which isprogrammed such that one of its data line output terminals provides achecker pulse enable (CPE) signal which is high during that portion ofthe picture period that the checker signal is to be present. A secondEPROM data line output terminal provides an end-of-field identification(EFI) signal which is high during the lines at the end of each fieldwhich will have to include vertical modification signals.

[0122] The horizontal-rate phase-locked loop component f_(H) is alsoapplied to a one-shot circuit OS2 which generates an end-of-line pulse(ELP) of the required duration of the checker pulses, typically 2 μs(see FIG. 7a).

[0123] The horizontal-rate phase-locked loop output signal f_(H) is alsoapplied to another one-shot circuit OS3, providing an output pulse ofapproximately 13 μs duration. The output of one-shot OS3 triggersanother one-shot OS4 with an output pulse VJP of approximately 52 μsduration. The timing and duration of pulse VJP define the position ofthe vertical modification inducing signal within the line time; i.e.pulse VJP is essentially on during the desired portion of the activehorizontal line period.

[0124] The four signals ELP, VJP, CPE and EFI generate the requiredcontrol signals for the signal selection switches 104-1, . . . , 104-4(see FIG. 6b). The end of line pulse ELP is applied to a divider circuit122 to derive the desired frequency to determine the checker frequency.The higher this frequency, the greater the number of checkerdark-light-dark transitions per picture height. This frequency may bechosen within a wide range; a divider ratio of 52 (n=52) provides auseful result. The divider 122 output signal is applied directly to oneinput terminal of 3-input AND gate U4. An inverted output signal ofdivider 122 is applied to the corresponding input terminal of second3-input AND gate U5. The output portino of divider 122 can be a sweeposcillator circuit consisting of a pair of NE566 IC's. One NE566 is setnominally at 300 Hz and the other is set at 1 Hz. The output of the 1 HzNE566 is fed to the frequency control input of the 300 Hz NE566. Both3-input AND gates U4, U5 have the checker pulse enable (CPE) and end ofline pulse (ELP) signals applied to their two other input terminals. Theresult is a high checker control (HVJ) signal at the output terminal of3-input AND gate U4, and a low checker control (LVJ) signal at theoutput of 3-input AND gate U5.

[0125] A similar arrangement generates the required signals for thevertical modification control signals. An oscillator 126 (such as thecommercially available part number NE555 or NE566) is configured tooperate at low frequencies, typically between DC and 10 Hz. Theoscillator 126 can be set to a high logic level output. Similarly the DCto 10 Hz signal output can be swept over a range of frequencies to upsetas many TV sets as possible during playback of an illegal copy. This canbe done as described above with a pair of NE566 IC's. The output signalof oscillator 126 is applied to one input of a 3-input AND gate U2. Aninverted output signal of oscillator 126 is applied to the correspondinginput terminal of a second 3-input AND gate U3. Also, each TV set may“resonate,” or jitter more at unique frequencies sweeping thefrequencies of oscillator 126 ensures wide coverage of different TVsets. The vertical jitter position (VJP) and end of field identification(EFI) signals (with signal EFI modified by flicker generator 130 and sodesignated EFI′) are applied to the other two input terminals of 3-inputAND gates U2, U3. The result is a high vertical jitter control (EFC H)signal at the output terminal of 3-input AND gate U2, and a low verticaljitter control (EFCL) signal at the output of 3-input AND gate U3.

[0126] It will be understood that with suitable modifications, the aboveapparatus will produce the added horizontal or vertical modificationsafter the normal horizontal or vertical sync signals, e.g. for the addedvertical modifications at lines 22-24 of an NTSC television signal, soas to cause a video retrace.

[0127] The circuit of FIG. 6b in conjunction with flicker generatorcircuit 130 via EFI′ produces multiple vertical modification signalpatterns.

[0128]FIG. 6b shows the field or frame “flicker feature” generator 130used in certain embodiments of the invention for modifying thehorizontal and vertical modifications.

[0129] The following are achieved by this flicker feature:

[0130] 1) Change the “polarity”, i.e., invert the gray vs. blackrectangles of the checker pattern at some particular multiple of fieldrate; this will for instance cause the attenuated video from anunauthorized copy to interleave the checker displacement, furtherdegrading the viewability of the copy.

[0131] 2) A field-by-field change of the position of the end of field(vertical modification) pulses causes the authorized copy to playback ona TV set an up/down flicked blur, because each field has a differentlytimed pseudo-critical sync pulse position. This is achieved for exampleif:

[0132] EFI pulse is high on lines 255-257, and

[0133] EFI1 pulse is high on lines 258-260, and

[0134] EFI2 pulse is high on lines 261-262 and 1, and

[0135] EFI3 pulse is high on lines 21-23.

[0136]FIG. 8 shows the circuitry of flicker generator 130 of FIG. 6b,and shows that these four pulses are multiplexed via multiplexer U10(i.e., a CD4052) at a field rate by EPROM U8 (part number 27C16 or2716). As a result, pseudo-vertical sync pulses occur differently inposition depending on the field. In a simple example, EFI, EFI1, EFI2,EFI3 are stepped once per field. As a result, during playback of anunauthorized copy, the pseudo-vertical occur at lines 256 or 259 or 262or 22 in successive fields or frames. As a result, the picture flickersbecause of the field rate vertical sync repositioning in the TV or VCR.EPROM U8 provides flexibility as to where the various end of fieldpulses are to be located as a function of time.

[0137]FIG. 8 also shows how the checker pattern black vs. grayrectangles are inverted at some particular multiple of field rate. Thevertical sync pulses clock the 8 bit counter U7 (divide by 256, partnumber 74HC393). The outputs of counter U7 drive the address lines ofthe EPROM U8. The data output signal DO from EPROM U8 goes high toinvert the checker pattern via switches SW1K, SW2K. The flexibility ofsignal DO from EPROM U8 allows the invert commands on the checkerpattern to happen pseudo-randomly or periodically, and also allowsdifferent flicker rates (i.e. every 2 fields or every 5 fields, etc.).EPROM U8 data lines D₁ and D₂ also drive multiplexer switch U10 (partnumber CD4052), similarly improving flexibility to generate outputsignal EFI′.

[0138] Another Circuit for Generating the Vertical and HorizontalModifications

[0139] In FIG. 6b the end of field and end of line pulses are switchedthrough to override the video driving resistor R₀. Unless these switcheshave a low enough “on” resistance, video from the input program sourcewill always superimpose on top of the end of field or end of linepulses. For example, a typical analog switch on-resistance is about 100ohms. The typical resistance R₀ is about 1000 ohms. With these values,10% of the video superimposes on the end of line and end of fieldpulses. If the video goes to peak white, the end of field and end ofline pulses will have a minimum of about 10% peak white (100 IRE) or 10IRE thus rendering these added pulses useless.

[0140] To overcome these possible shortcomings, in another embodimentthe added pulses are added then switched in via multi-pole switches thatat the same time switch out the video source.

[0141] As shown in FIG. 9, the end of field high and low states aregenerated by AND gate U23 with input from oscillator U22 (a 0.1 Hz to 10Hz oscillator) and input signals VJP and EFI. Switch SW103 switchesbetween the high and low states controlled by variable resistors R_(B)and R_(A) respectively. Amplifiers A10A, A10B are unity gain bufferamplifiers. To ensure against crosstalk of low states of EOF and checkerpulses, switch SW103A is connected between switch SW103 and amplifierA100, and switch SW102A is connected between switch SW102 and amplifierA101. Gate U23A “and” gates switch SW103A to go to ground on all linesother than the EOF line locations. Likewise, gate U21A gates switchSW102A to ground at all times other than when the checker pulses are on.Otherwise, switches SW103A and SW102A are transparent to the EOF andchecker pulses of switches SW103 and SW102, respectively. The output ofswitch SW103 is buffered by unity gain buffer amplifier A100 and summedinto a summing amplifier A102. Similarly, switch SW102 receives the endof line high, low states generated via signal ELP, counter U20 (a divideby n counter), and signal CPE.

[0142] Variable resistors R_(C) and R_(D) provide adjustment for highand low end of line pulses respectively. Amplifier A101 buffers switchSW102 into summing amplifier A102 via resistor R2. Amplifier A102 feedssumming amplifier A103. The post pseudo-sync pulse (PPS) is also summedinto summing amplifier A103. The output of summing amplifier A103 isthen: end of line pulses, end of field pulses and post pseudo-sync pulse(PPS). Switch SW101 switches in all of these pulses via OR gate U10 andinverter U11 during their coincident times, and switches in video at allother times. Amplifier A104 buffers output of switch SW101 and provide avideo output “Video Out” containing video with the added pulses. SwitchSW104A preblanks to video from the sync narrowing circuit to a voltagelevel VBLNK (i.e. O IRE) for the last active 9 lines of each TV fieldvia “AND” gate U104B. Gate U104B has EPROM data output EFO (which turnshigh during the last 9 lines of the TV field) and VJP (active horizontalline pulse) at its two inputs.

[0143] A position modulation source for the PPS is controlled by voltagesource Vgen. Source Vgen feeds resistor R20 with an inverted burst gatepulse into resistor R10 and capacitor C2 to form a variable delay intoone shot U20. One shot U20 is approximately 1.5 μsec of variableposition after burst of input video, and is gated out during thevertical blanking interval by signal CPE and NAND gate U21B. Resistor R6determines the amplitude of the PPS. Resistor R6 is typically set to −10IRE to −20 IRE. The other input (U22A) of “NAND” gate U21 is normallyhigh as to all PPS to be a constant amplitude pulse position sync. IfU22A is pulsing (i.e., 300 Hz), the PPS signal is then turning on andoff as well (at 300 Hz). Thus, the PPS can be a position modulatedpulse, and pulse amplitude modulated sync pulse following burst.

[0144] Horizontal Sync Pulse Narrowing Modification

[0145] A sync pulse narrowing circuit and method for enhanced of ananticopy protection of video signals is used by itself or in cascade (asshown in FIG. 6a block 96) with any of the above-described other signalmodification techniques, and as further described below. The reason tonarrow the video signal sync (synchronization) pulses (mainly thehorizontal sync pulses) is so that when an illegal copy is made, theattenuated video with reduced sync pulse width (duration) causes aplayability problem when viewed on a TV set. This is because most TV setsync separators incorporate sync tip DC restoration. Because these TVset sync separators are typically driven by medium impedances, the syncpulses are partly clipped off. By narrowing the sync pulses, the syncpulses are even further clipped off. When an unauthorized copy is madeof the video signal, especially with the above-described checker and/orend of field modification signal, the copy has a reduced amplitude videowith reduced sync pulse width. As a result, the TV sync separator sees asevere loss in sync due to its own clipping from the narrowed sync widthand the attenuation of the video itself. Thus, the TV set's syncseparator does not “extract” sync properly and this causes the TVpicture to be even less viewable, because the horizontal and/or verticalmodification effects are more intense.

[0146]FIG. 10 shows a typical prior art sync separator as used in manyTV sets. This circuit operates when the inverted video is fed to thebase of the transistor Q1 via a coupling capacitor C. The sync tips ofthe video signal charge up the capacitor C, just enough so that only thevery tip of the sync pulses turn on the transistor. Resistor R_(b)biases the transistor so that the tips of sync are “sliced”. The voltageVc across C, is related to resistance R_(o) the driving resistance ofthe video. The larger resistance R_(o), the more the amount of syncclipping is seen at V_(b). If resistance R_(o) is too large, thetransistor Q1 will start sync slicing into the video (blanking level)region, because the value of V_(c) is not charged up to an average levelto allow a cut off of the transistor just below the sync tip level ofinverted video.

[0147] Insufficient charging of capacitor C allows transistor Q1 to beturned on even when blanking level arrives. The base emitter impedanceof transistor Q1 is low when transistor Q1 is on. (This causesattenuation of the positive going sync pulses). Since charging capacitorC is a function of the sync pulses' width, narrowing the sync pulsesmakes the sync separator clip a portion of the narrowed sync more than anormal sync width. This is equivalent to sync slicing at a point closerto the video signal (i.e. video blanking level). Under normal videolevels a narrowed sync pulse presents no playability problems on a VCRor TV. But when a narrowed sync pulse is recorded on an illegal copy ofa copy protected cassette, the video signal is attenuated. Thisattenuation with the narrowed sync causes the TV (during playbackviewing) to not reliably extract the sync pulses and instead synchronizeoff parts of the video signal, i.e. blanking level.

[0148] Selectively narrowing certain horizontal sync pulses to close tozero pulsewidth (to less than 600 ns duration) so that the filter in aTV or VCR sync separator does not respond or that the sync separatorcoupling capacitor charges up negligibly is equivalent to there being nosync pulse in that area. These selected horizontal sync narrowed pulsesnear the end of the field can create a situation such that the syncseparator will slice a blanked video line as a new (spurious) verticalpulse during playback. With a video signal from an illegal copy withattenuated video supplied to the TV, this situation then causes the VCRor TV to see two vertical pulses in one field, which can cause verticaljitter.

[0149] In one embodiment, the pulsation (modulation) frequencies of theend of the video field lines (those end of field lines having anamplitude 0 IRE to at least 10 IRE having narrowed horizontal syncpulses) are swept from about 1 Hz to 15 Hz. This advantageously causesthe desired effect in a wide variety of TV sets.

[0150]FIG. 11a shows a video signal waveform (Vin); this is inverted thevideo into the TV sync separator circuit in FIG. 10, and is coupled toresistor R_(o) (where R_(o)≈0) of FIG. 10. FIG. 11b shows the effect ofthe coupling capacitor and resistor R_(b). Note at Vb the video signalis ramping up towards the sync tip level. (This is a result of the RCtime constant of resistor Rb and capacitor C since Rb>>Ro.)

[0151]FIG. 11c shows narrowed horizontal sync pulses. The action ofresistor R_(o) (where R_(o) now is medium resistance i.e. 200 to 1500ohms), capacitor C, resistor R_(b) and transistor Q1 cause clippingaction of the narrowed sync tip. Because the sync widths are narrower,capacitor C is not charged up sufficiently and causes more syncclipping. Recall that the charging of capacitor C is related to both theamplitude of the sync pulse and its pulse width, i.e. Vc is proportionalto (sync pulse width) multiplied by (sync amplitude). The lower thevoltage Vc the more the sync clipping action. FIG. 11d shows this resultat point in FIG. 10 Vb.

[0152]FIG. 11e shows an attenuated video source signal from an illegalcopy with narrowed sync pulses where “A” indicates the presence of thechecker pulses. The sync separator responds by clipping the sync pulsescompletely and as a result, parts of the video toward the end of lineare interpreted as new sync pulses. FIG. 11f shows this. The syncseparator (inverter) transistor Q1 turns on during the clipped portionof video.

[0153]FIG. 11g shows that by slicing parts of the video, the leadingedge of sync is rendered unstable. This leading edge instability of thesync separator causes the TV to display an unstable image (i.e., shakingside to side). As shown by the arrows, the resulting unstable horizontalsync pulses are caused by sync narrowing or checker pulses.

[0154]FIG. 11h shows what the output of the TV sync separator would havebeen for FIG. 11d, which is a full level TV signal with narrowed sync.Thus the signal of FIG. 11d poses no playability problems to a TV set.Only when the signal of FIG. 11d is added to a copy protection signaland an illegal copy is made do playability problems become evident onthe TV set, because the illegal copy results in an attenuated signal.

[0155]FIG. 11i shows with a full unattenuated TV signal that if selectedlines near the end of a video field or after the vertical sync pulses(i.e. NTSC lines 256-259, lines 10-12) are narrowed with varyingamplitude (i.e. switching from about blanking level to about 10-100IRE), the sync separator transistor Q1 will start ramping up to sliceinto the picture area, i.e. “ZZ” of FIG. 11j. This causes a wider pulsein the “ZZ” area, but not wide enough to cause a vertical sync pulse.

[0156]FIG. 11k shows the sync separator output of the waveform of FIG.11j. If this waveform is to be accompanied by anticopy protectionsignals, the illegal copy will provide an attenuated signal to the TVsync separator as in FIG. 111. FIG. 111 is an attenuated TV signal dueto illegal copying with narrowed syncs accompanying the end of fieldlines.

[0157]FIG. 11m shows the ramping action at point V_(b) via resistor Rband capacitor C. The corresponding output of the sync separator shows at“y” a new (spurious) broad (vertical sync) pulse. This newpseudo-vertical sync pulse has been created when the narrowed horizontalsync pulses are with the end of field lines at blanking level. When thenarrowed horizontal sync pulses are accompanied with 10 to 100 IRE, theTV sync separator only outputs narrow horizontal rate sync pulses, andno new broad pulses. This is because the 10 to 100 IRE levels areignored entirely by the sync separator. By the switching in and out ofblanking and greater than 10 IRE unit signals, the sync separator seesnormal vertical sync sometimes followed by a spurious early or latevertical sync pulse (see FIG. 11n). These spurious early and/or latevertical pulses then cause the TV to jitter up and down when playingback an illegal copy.

[0158] In some cases to get the same effect as above one can:

[0159] Narrow selected sync pulses to about zero, i.e. eliminatehorizontal sync pulse so as to make TV sync separator to make spuriousvertical sync pulse.

[0160] Reposition a few sync pulses with greater than 63.5 μs periods tocause the sync separator to malfunction and make a new spurious verticalsync pulse. This causes the ramping action of some sync separators tocause spurious vertical pulses.

[0161]FIG. 11o shows a video signal which is free of spurious verticalsync pulses due to a video signal being above blanking, i.e. greaterthan about 10 IRE units in the area of the narrowed pulses. Thus if thelevel of the video signal is high enough relative to blanking level, thepresence of narrowed horizontal sync pulses fails to generate a spuriousvertical sync pulse.

[0162] As shown in the sync pulse narrowing circuit of FIG. 12a, thevideo input signal (possibly already carrying the basic copy protectionpulses) is input to terminal 160 where it is supplied to sync separator162 and also to video adder 164. Sync separator 162 outputs separatedhorizontal sync (H sync) and vertical sync signals to line selector gate166 which selects for instance lines 10 to 250 of each video field. Theseparated H sync pulses are also provided to one-shot circuit OS10 whichin response outputs a signal of about 2 μs duration to AND gate U12, theother input of which is a line select signal indicating selected lines10 to 250 from gate 166. In response, AND gate U12 outputs a signalrepresenting a portion of H sync on each of these lines 10 to 250, whichis scaled by amplifier 174. The output of scaling amplifier 174 issummed back into the original video signal at adder 164, the output ofwhich is supplied to video out terminal 180.

[0163]FIG. 12b shows a representation of the waveform at point Q of FIG.12a (the conventional H sync signal with color burst), and the signal atR which is the output of scaling amplifier 174. The summed result of Qand R (“video out” at lower part of FIG. 12b) is seen at the video outterminal 180, which is a shortened H sync pulse with color burst.

[0164] Another circuit to perform sync narrowing with extended colorburst envelope (extended burst is necessary to ensure color lock for TVsets if narrowed H syncs cause a color lock problem) is describedhereinafter. FIG. 13a, 13 b show a circuit for introducing narrowedhorizontal sync pulses throughout the active video field. Within thisactive field, an EPROM data output determines which lines get narrowedfurther. For example, this EPROM output (EPD1) can allow for lines20-250 to have a 3.7 μs sync replaced pulse width, while lines 251-262have a 2.0 μs sync replaced pulse width. Other combinations are possibledependent on programming EPD1 in EPROM U9. Also, another output fromEPROM U9 can cause sync suppression in lines (i.e., lines 255 and/or257) or so, before the location of the EOF pulses (this is done via ANDgate U10 and EPD2 from EPROM U9). Repositioned horizontal sync narrowedsync is also possible after sync suppression in normal HBI is done.

[0165] Input video carrying any combinations of: the basic anticopyprocess, end of field pulses, and checker process or normal RS170 typevideo is DC sync restored by video amplifier A1 to OV (equal to blankinglevel). Amplifier A1 outputs into sync separator circuit U2 which inturn outputs composite sync and a vertical pulse between 1 μs and 20 μs.To generate a burst gate to lock input video's burst to circuit 2015,care must be taken not to generate a burst gate pulse when pseudo syncpulses are present (i.e., if input video has the basic anticopyprocess). Thus, one shot U3 takes composite (and pseudo) sync and oneshots a non-retriggerable pulse of about 45 μs, long enough to ignoreequalizing and vertical 2H pulses in the vertical blanking interval andalso the pseudo sync pulses that may be present (usually in the first 32μs of the TV lines 10-20). One shot U10 delays the leading edge of inputvideo sync by 5 μs and triggers one shot U11, a 2 μs one shot to becoincident with the input video's color burst.

[0166] Amplifier A1 drive a chroma bandpass filter amplifier A91 toinput into burst phaselock loop circuit 2105. The output of PLL circuit2105 is now a continuous wave subcarrier locked in phase with the inputvideo's color burst. PLL Circuit 2011 adjusts the regenerated subcarrierphase to be correct at amplifier A5 output. Frame sync pulse from syncseparator U2 resets address counter U8 for EPROM U9. Counter U8 isincremented by a horizontal rate pulse from amplifier A3. EPROM U9outputs each data line that contain particular TV lines high or low inthe active field.

[0167] One of the advantages of the circuit of FIGS. 13a and 13 b isthat the regenerated narrowed sync can be placed anywhere in thehorizontal blanking interval (HBI). This becomes advantageous especiallyif the new narrowed sync can start 1 μs in advance (before) inputvideo's horizontal sync. With a 1 μs advance in new narrowed horizontalsync and the PPS pulse, the horizontal instability with an illegal copyhaving the basic anticopy process results in 1 μs more in horizontaljitter. By advancing the narrowed H sync pulse, a greater time distanceexists between the narrowed H sync pulse and the PPS, yieldingproportionally greater instability when an illegal copy is played back.

[0168] To generate an advance narrowed H sync, the output of one shot U2is a 45 μs pulse coincident with the leading edge of input sync is“squared” up via 32 μs one shot U4. The filter including components R1,L1 and C1 bandpass filters the output of one shot U4 into a 15.734 KHzsine wave.

[0169] By adjusting inductor L1, a sinewave in advance (or behind) ofinput video's H sync is produced. Comparator A3 converts this sinewaveinto pulses whose edges are leading or lagging the video input's leadingsync edge. The “tracking” ability of filter R1, L1, C1 (with a Q of 4)to generate waveforms synchronous to the input video is, in general,better than most horizontal PLL's when the video input is from a VCR.The output of amplifier A3 then goes to 14 μs one shot U5, to generatean HBI gate signal to replace old (input) sync and burst with newnarrowed sync and extended burst.

[0170] One shot U6 sets a nominal narrowed sync delay of 0.5 μs from thebeginning of the input video HBI (of one shot U5's leading edge) and oneshot U7 triggers off a new narrowed sync pulse. Components R2, R3 and Q1form a switch to narrow the pulse further by shorting out transistor Q1(emitter to collector) and via command of EPD1 (i.e., for lines 251-262each field EPD1 is low, and high elsewhere). The output of one shot U7is then pulses of 3.7 μs from lines 20 to 250 and pulses of 2 μs from251 to 262. Triggering off the trailing edge of one shot U7 is one shotU12, the output of which is the extended burst gate which (about 5.5 μspulse width).

[0171] The output of one shot U12 gates a color burst from circuit 2011via switch SW22, and the band pass filter (3.58 Mhz) amplifier A4 shapesthe extended burst envelope from switch SW22 output and couples tosumming amplifier A5, via extended burst amplitude adjustment resistorR10. Narrowed H sync from one shot U7 is “anded” via gate U13 withsignal EPD2 which is generally high, except for the few lines on whichnarrowed sync is to be suppressed, which enhances the end of fieldpulses. The output of gate U13 sums into amplifier A5 via narrowed syncamplitude control resistor R8. The output amplifier of A5 is thennarrowed sync plus extended color burst. Switch SW25 switches the outputof amplifier A5 via AND gate U14 through OR gate U20, which switchesamplifier A5 output during the HBI via one shot U5 output and EPD3,(active field location pulses i.e., lines 20-262).

[0172] Buffer amplifier A22 then outputs video from input with newnarrowed H sync and extended color burst. To gate in a repositioned syncpulse (EOFRSP) in the end of field location, one shot U16 is 10 μs to 40μs in length from the leading sync edge of input video. Gate U16 couplesto gate U17 a 2 μs to 4 μs wide pulse that is delayed about 10 μs to 40μs from the input video's leading sync edge. The output of gate U16 isenabled via AND gate U18 and EPD4 from EPROM U9. Signal EPD4 is thenhigh at certain lines at the end of the field after sync suppression isactivated via EPD2. Gate U16 drives summing amplifier A5 via EOFRSPamplitude adjustment resistor R85. Gate U16 also turns switch SW25 onduring activation of EOFRSP through OR gate U20 to insert therepositioned sync pulse (EOFRSP). Thus the output of amplifier A2 hasinput video, narrowed sync and possibly 1 or 2 lines of suppressed sync(no sync) or/and a few lines of repositioned narrowed H-sync.

[0173] The sync pulse narrowing is effective even if not all horizontalsync pulses in a video signal are so narrowed. It has been determinedthat even a relatively small number of narrowed horizontal sync pulsesprovide a spurious vertical retrace. For instance, three to sixconsecutive video lines with a narrowed horizontal sync pulse areadequate for this purpose. It is preferred to group together thenarrowed horizontal sync pulses in consecutive (or at least relativelyclose together) lines to generate the spurious vertical retrace.

[0174] Other circuitry for sync pulse narrowing, in the context ofremoval of copy-protection signals, is disclosed in U.S. Pat. No.5,157,510, Ron Quan et al., and U.S. Pat. No. 5,194,965, Ron Quan etal., both incorporated by reference.

[0175]FIGS. 14a and 14 b show block diagrams of two apparatuses forcombining the above described sync pulse narrowing with the earlierdescribed prior art copy protection process and horizontal and verticalsignal modifications.

[0176]FIG. 14a shows the first such apparatus, with program videosupplied to circuitry block 204, for adding the prior art copyprotection signals including the added AGC and pseudo-sync pulses. Thenext block 206 (shown in detail in FIG. 6a) adds (1) the checker patternand (2) the vertical rate signal modifications to the end of each ofselected fields. Then the sync pulse narrowing circuitry block 208(shown in varying detail in FIG. 12a and FIGS. 13a and 13 b) furthermodifies the video signal, which is output at terminal 209, forinstance, to a master duplicator VCR in a video cassette duplicationfacility. It has also been observed that the prior art basic anticopyprocess was improved by just adding in conjunction the sync narrowingprocess.

[0177] Alternatively, in FIG. 14b the input program video signal isfirst subject to the sync pulse narrowing circuitry block 208, and tothe copy protect and checker pattern and vertical rate signalmodification circuitry blocks 204, 206 (shown here combined into oneblock) and hence supplied to output terminal 210.

[0178] It is to be understood that other apparatuses may also providethe disclosed video signal modifications, i.e. the checker pattern, endof field vertical pattern, sync narrowing, and equivalents thereof.

[0179] Method and Circuit for Removal of Video Copy Protection SignalModifications

[0180] Given an anticopy process signal including at least AGC andpseudo-sync pulses as described above and/or sync narrowing, and/or endof line “checker” pulses, and/or end of field pseudo-vertical syncpulses, a method and circuit for defeating these is describedhereinafter.

[0181] For the AGC and pseudo-sync pulses, Ryan, U.S. Pat. No. 4,695,901and Quan U.S. Pat. No. 5,157,510 both incorporated by reference,disclose methods and apparatus for defeating (removal or attenuation of)these added pulses. Ryan, U.S. Pat. No. 4,695,901 discloses only theremoval or attenuation of pseudo-sync and AGC pulses, and does notdisclose the defeat of sync pulse narrowing, end of field pseudovertical sync pulses, or end of line (checker) pulses. Processingamplifiers as are well known in the art can remove sync pulse narrowingwith regenerated sync, but processing amplifiers do not defeat the endof line checker pulses or end of field pseudo-vertical sync pulses.

[0182] It is not taught in the prior art how to defeat these copyprotection vertical and checker signals. Merely blanking them out canstill cause residual anticopy signal enhancements to survive when anillegal copy is made. The reason is that blanking these signals toblanking level alone in the presence of pseudo-sync and AGC pulses willcause an attenuated video signal to be input into a TV set when anillegal copy is made. This attenuated signal then has, for instance, endof field lines at blanking level and can cause pseudo-vertical syncpulses in this situation. This is true especially if narrowed horizontalsync pulses are still present.

[0183] On the other hand, if only the narrowed sync pulses are restoredto normal sync width, the other two copy protection enhancement signals(checker and vertical) are still effective.

[0184] Thus the following methods defeat the above disclosed anticopyprocess enhancements:

[0185] 1) The end of line (checker modification) copy protection signalsare replaced with a signal at least about 20% of peak white, or a levelshifting signal of at least 20% of peak white is added to the end ofline signal. The signal replacement or adding may be to a portion of thechecker signal so as to defeat the process. By “portion” is meant thepart of the end of line pulse to be “neutralized” or part of all thelines of video that has the end of line pulses.

[0186] 2) The end of field (vertical) copy protection pulses arereplaced with a signal that is at least about 20% of peak white for aperiod of at least around 32 μsec per line; alternatively a levelshifting signal of at least about 20% of peak white is added to thevertical pulses for at least around 32 μsec on enough lines (i.e. 7 of9, 5 of 7, 2 of 3) to defeat the anticopy process.

[0187] It is to be understood that the 20% of peak white level referredto here with respect to the vertical and checker pulses has beenexperimentally determined to be a typical minimum value needed toproduce the intended effect of defeating the video signal enhancements,and that a higher level signal (such as 30% or more) would accomplishthe purpose even more thoroughly.

[0188] 3) Most (50% or more) of the narrowed horizontal sync pulses arewidened so as to defeat the sync narrowing process, i.e. if sync isnarrowed to 3.0 μsec, a widened sync pulse to 4.0 μsec may be adequateto defeat the sync narrowing process, and without the need to replacethe narrowed sync with RS170 standard horizontal sync pulses. (Note that4.7 μsec is specified as the horizontal sync pulse width for the RS170standard.)

[0189] 4) A widened sync pulse width encroaching into the end of line(checker) pulses can be used to defeat both the checker and syncnarrowing processes. Care must take to assure that the flyback pulse ofthe TV set still triggers color burst, because widening the sync pulseto include part of the checker pulses can cause the TV set's flybackpulse to trigger prematurely.

[0190] 5) A horizontal sync and colorburst with adequate sync and burstwidth repositioned into the checker pulses can defeat both the syncnarrowing and the checker processes, without causing the TV set'sflyback signal to trigger incorrectly the TV set's color burst signal.

[0191] The vertical pulses will have the effect of vertical sync signalson a TV set if reduced video amplitude is present. Most TV sets or VCRsneed about 30 μs to trigger the vertical sync filter to output avertical pulse. Thus, by modifying the vertical pulses such that even ifresidual pseudo-vertical pulses are of less duration than for instance20 μs, then no pseudo-vertical sync pulses are output from the verticalsync filter.

[0192] Sufficient defeat of the checker pulses results if the “low”state of the checker pulse is shortened so as to cause a narrowedhorizontal sync pulse not to be detected by the TV set's or VCR's syncseparator. This avoids the effect of the checker pattern when playingback in an illegal copy.

[0193]FIG. 15 shows a two step circuit and method for removing all theabove-described anticopy protection signals. A video signal containingAGC, pseudo-sync, checker, vertical pulses, and narrowed horizontal-syncpulses is first input on terminal 228 into the circuitry 230 asdisclosed in Ryan, U.S. Pat. No. 4,695,901 or Quan, U.S. Pat. No.5,157,510 to defeat the effects of the AGC pulses and pseudo-syncpulses. Second, the output signal from circuitry 230 is input into theenhancement remover 234 which defeats the checker and vertical pulses,and also defeats sync narrowing and any residual AGC pulse orpseudo-sync pulses in the horizontal blanking interval. The video andsignal at terminal 236 is thus free of all effects of copy protectionsignals.

[0194] In this embodiment, the checker and vertical pulses are defeated(ideally) by replacing these pulses with pulses having an amplitude ofabout 20% of peak white pulses, or by adding a level shifting signalhaving an amplitude of about 20% of peak white. The checker pulses canalso be defeated by substituting in a wide horizontal sync signal,thereby replacing the checker pulses. This defeats the checker pulsesand widens the horizontal sync pulse to defeat the sync narrowingprocess. Finally, if the HBI (horizontal blanking interval) is replacedby new horizontal sync and color burst, then the sync narrowing and anyAGC pulse and/or pseudo-sync pulse in the active field are defeated.

[0195] Also in this embodiment, narrowing the black level duration ofthe checker and vertical pulses results in a viewable copy. Also, anyAGC pulses following a normal horizontal sync pulse can be defeated byadding a negative level shifting pulse to counter the elevated colorburst (AGC pulse) or by sync and burst replacement. A circuit foraccomplishing this is described hereinafter. In FIG. 16, showing detailsof block 234 of FIG. 15, an enhanced anticopy protected signal is inputto amplifier A10 having gain K (i.e. K is equal to 2). The output ofamplifier A10 is coupled to capacitor C1, diode D1, and resistor R1,which together are a DC sync restoration circuit. Resistor R2, capacitorC2, and capacitor C1 form a color subcarrier frequency notch filter sothat comparator A11 can separate sync properly. Voltage reference Vb1sets the slice point to cause comparator A101 to function as a syncseparator. The output of comparator A11 is then fed to a low pass filterincluding components resistor R3, inductor L1 and capacitor C3 torecover a vertical rate pulse. Comparator A12 with reference input levelV_(b2) is a vertical sync separator.

[0196] Because this video signal can be from a VCR, certain syncseparators, i.e. the LM 1881, produce incorrect frame pulses with VCRoutputs. So to generate a frame pulse, one shot U1 outputs a pulse thatends slightly short of six lines from the beginning of the firstvertical sync pulse. One shot U2 outputs pulse having a width of about25 μs.

[0197] Then AND gate U7 logically “ands” the output of inverter U6 withthat of one-shot U2 to generate a pulse occurring every two fields oreach frame. Only in one field is output from U2 and U6 high. Gate U7'soutput is the signal (FID) gate which triggers (see FIG. 17) one shot U8having a pulse duration of 1½ fields. With D flip flop U9 and with theoutput of one shot U8 connected to the D input of flip flop U9 andvertical sync as the clock input for flip flop U9, a frame rate squarewave is produced with its rising and falling edges coincident with thefirst vertical sync (broad) pulse of the incoming video signal. One shotU10 with counter circuit U11 and horizontal rate pulse from horizontalPLL U4 generates signals on a 10 bit address bus B10 that counts 525states. EPROM U12 is addressed by 10 bit bus B10, and dependent on howEPROM U12 is programmed, EPROM U12's output lines carry the followingsignals:

[0198] 1) Active field location (AF) (high states from line 22 to line262).

[0199] 2) End of field location (EOFL) (high states from line 254 to262).

[0200] In FIG. 16, PLL circuit U4 and one shot U5 are a horizontal ratePLL circuit such that PLL circuit U4's output is in advance of theleading edge of video horizontal sync by about 3 μs. This is done by oneshot U5, which delays PLL U4's output by about 3 μs. The output of oneshot U5 is fed back to a phase detector input of PLL U4. Since the edgesof both detector inputs of PLL U4 must match, PLL U4's output must thenbe in advance of the leading sync edge amplifier (comparator) A101. PLLU4 also ignores any pulses other than horizontal rate. Thus verticalpulses and others are ignored by PLL U4.

[0201] Furthermore, one shot U3 develops a burst gate pulse (BG) ofincoming video by timing off the trailing edge of sync from comparatorA11.

[0202]FIG. 18 shows a level shifting circuit defeating the checker andvertical pulses. Amplifiers A20, A21 form a summing amplifier. Signalssupplied to this summing amplifier are via resistor R100 for video, viaresistor R101 for end of line pulses, and via resistor R102 for end offield pulses. By using the advance horizontal pulse (AHP) which startsat the same time as each of the checker pulses, a pulse of about 1.5 μsduration is timed off the AHP using the active field pulse AF from EPROMU12. AND gate U13 generates a logic high pulse (EOLD) at the end of eachline during the active field. This pulse from gate U13 then is added tothe video, which causes the checker pulses never to come down toblanking level. Instead, the checker pulses now have a minimum 20% ofpeak white level. This defeats the end of line checker pulses becauseunder the circumstance of an attenuated video signal, the checker pulsesdo not go down in video level enough to cause a sync separator to“accidentally” trigger.

[0203] Similar results are achieved for the vertical pulses where oneshot U16 generates an active horizontal line pulse of about 49 μsduration (a minimum of 35 μsec) via the AHP into one shot U15 for apulse that ends at the HBI. One shot U16 then triggers off one shot U15(14 μsec pulse duration) to form an active line pulse. This activehorizontal line pulse is and'd by gate U150 with the end of fieldlocation (EOFL) pulse via EPROM U12. The EPROM U12 EOFL pulses send ahigh logic signal at the end of the field during the horizontal activeline via gate U150. This high logic level from gate U150 output is thenadded to the video signal by resistor R102 to ensure that the verticalpulses are at a minimum level of 20% of peak white. With the verticalpulses having a level of at least 20% of peak white, under attenuatedvideo circumstances, these new end of field lines will not cause apseudo-vertical sync. The output of amplifier A21 then contains defeatmechanisms for both checker and end of field pulses. To defeat the syncnarrowing process, the output of amplifier A21 is coupled to capacitorC12, capacitor C13, diode D10, diode D11, and resistor R12, which form aDC sync tip amplifier. Voltage VD2 is set to have 0 volts DC at blankinglevel into amplifier A22.

[0204] By using AHP again, one shot U17 and one shot U18 generate a newwidened sync pulse. Components R17, C18, C3, C19, R18 and R19 are a lowpass filter for finite rise time sync. Voltage V_(b3) is set toestablish blanking level for the “high” state of new widened sync. Oneshots U19 and U20 with AND gate U21 are the control logic to reinsertthe new wider horizontal sync pulse during the active field. The outputsof one shots U19 and U20 are slightly delayed from U17 and U18 toaccommodate the delay in the lowpass filter including components R17,C18, L3, etc. Electronic switch SW1 thus switches in the widened syncand outputs video out to amplifier A23. The right hand portion of FIG.18 within the dotted line is the sync replacement and output circuitryS50.

[0205]FIG. 19 shows a circuit to be used in conjunction with that ofFIG. 16 that replaces the checker pulses with new widened horizontalsync pulses and a new color burst to follow these new widened horizontalsync pulses. Also the vertical modification pulses are defeated by levelshifting via source signal EOFD (from FIG. 18) into resistors R412 andR411.

[0206] Input video is fed to a chroma band pass filter includingcomponents R299, C400, L400 and C401 into burst regenerator U40 (partnumber CA1398) which is a burst to continuous wave subcarrier (3.58 mhz)regenerator; crystal Y40 is a 3.58 mHz crystal. The output of burstregenerator U40 is filtered via a band pass filter (3.58 mHz pass,including components R300, L401 and C402) and buffered by amplifier A40.Electronic switch SW40 gates in new color burst via one shot U43. Oneshot U43 is triggered by the trailing edge of the regenerated widenedsync of one shot U41. One shot U40 is a 0.5 μs delay to establish ahorizontal sync front porch “breezeway”. Regenerated sync from one shotU41 output is filtered and level shifted via components R307, L403,C404, R305, R306 and voltage V400. Amplifier A42 buffers this levelshifted widened regenerated sync to sum in with color burst via resistorR304 and amplifier A43. Electronic switch SW41 gates in during theactive field (via AND gate U44 and the AF source signal from EPROM U12)new widened sync and new burst during the HBI. (The new widened sync andnew burst also defeats any anticopy video signals with active field AGCpulses in the HBI, i.e. raised back porch pulses). Amplifier A44 buffersand outputs new video with defeated anticopy signals including narrowedsync, checker pulses, vertical pulses.

[0207]FIG. 20 shows a circuit for “level shifting” by multiplying anon-zero voltage to a higher voltage. End of line defeat signal EOLD andend of field defeat signal EOFD are used for level shifting in FIG. 16generate a control voltage to raise the gain of voltage controlledamplifier (VCA) U50 (part number MC1494) during the presence of checkerpulses and vertical modification pulses in the copy protected signal.The video is DC restored so that sync tip is at 0V, which means lowstates of the checker and vertical modification pulses are above 0V(typical from 0.3V to 0.5V). Components C201, R201, D10, D20, C200, R200and A49 form this DC restored video signal. The output of VCA U50 thenhas a equivalent level shifted or amplified anticopy signal well aboveblanking level to defeat the anticopy enhancements. Amplifier A50buffers the output signals from VCA U49 into the narrowed sync pulsedefeat circuit of FIG. 16.

[0208]FIGS. 21, 22, and 23 show alternatives to defeat the checker andvertical anticopy signals by switching circuitry.

[0209]FIG. 21 shows that (for the DC restored video of FIG. 16) duringthe checker and vertical pulses, control voltages coincident with thesepulses switch in (under control of the EOLD and EOFD signals) a 20% ofpeak white signal V₁₀, overriding the anticopy pulses by electronicswitches respectively SW199 and SW198. The finite driving impedance ofthe video signal allows for this (resistor 200 providing the impedanceof about 2000 ohms). The video signal is then amplified by amplifierA501, and processed by the sync replacement and output circuitry S50 ofFIG. 18, before being outputted at terminal 506.

[0210]FIGS. 22 and 23 show alternative switching circuits to that ofFIG. 21 to defeat checker and vertical pulses. (Sync replacement andoutput circuitry S50 is not shown in FIGS. 22, 23 but is present as inFIG. 21). In FIG. 22, the DC restored video input signal is againapplied via resistor R201 to amplifier A54, with override switchesSW198, SW199 under control respectively of the EOLD and EOFD pulsesswitching in voltages V1, V2, each of which is a DC or DC offset ACsignal greater than or equal to 20% of peak white. The circuit of FIG.23 is similar to that of FIG. 22, except that switches SW198, SW199 arelocated serially directly in the video signal path and use conventionalreplacement means to overcome the checker and end of field pulses. Incertain cases merely blanking the checker and EOF pulses (blanking levelV₁=V₂=V₁₀) may be sufficient in a viewable copy to defeat the effects ofchecker or EOF pulses.

[0211] Apparatus to Defeat Horizontal and Vertical Enhancements by SyncWidening.

[0212]FIG. 24a shows a circuit with copy protected video with vertical(EOF) and checker (EOL) enhancements provided to input buffer amplifierA60 for defeat of the checker and vertical enhancements by sync pulsewidening. The output of amplifier A60 is coupled to sync separator U61.The composite sync output of sync separator U60 is fed to one shot U61to eliminate 2H pulses in composite sync. The output of one shot U64 isfed to PLL oscillator U65. The PLL's U65 frequency for N=910 is 14.31818MHz, equal to N times the horizontal line frequency (Nf_(H)). By usingNf_(H) to clock counter U68 and f_(H) to reset it, EPROM U69 receives a11 bit address bus from counter U68. EPROM U69 now can output horizontalpixel locations (as programmed into EPROM U69). The outputs of EPROM U69contain the horizontal timing for:

[0213] Pre-pseudo sync location

[0214] Sync widening location

[0215] New Burst gate location

[0216] Pseudo sync locations for EOF pulse

[0217] The output of sync separator U61 also has a field ID (Frame)pulse which resets a 525 state counter U63. State counter U63 is clockedby a horizontal frequency pulse by the PLL U65 and divided by N counterU607. EPROM U66 then has the horizontal line locations within the activeTV field. For example: in EPROM U66, D₀=lines 22-253 and D₁=lines254-262, the location of the vertical modification pulses.

[0218] Referring to FIG. 24b, logic gates U610 to U614 utilize the dataoutputs of EPROMs U69 and U66 for the following:

[0219] 1) Pre-pseudo sync and sync widening locations are gated throughsignal DO for pre-pseudo sync and widening sync (H) to be on lines22-253. The output of gate U613 does this.

[0220] 2) A sync widening only on lines 254 to 262 plus added pseudosync pulses only on lines 254 to 262; U612 output accomplishes this. ORgate U614 combines the outputs of gates V612 and U613 and ORs these withD3H, the new burst gate signal. The output of gate U614 controls switchSw600 to insert:

[0221] Pre-Pseudo Sync (Lines 22 to 253)

[0222] H Sync Widening (Lines 22 to 262 New Burst Gate)

[0223] 3) The new burst gate signal from signal D3H also, and D3 theactive field pulse, gates the signal fsc cw via amplifier A65 and ANDgate U615. The output of gate U615 is color subcarrier which is on onlywhen signals D3H and D3 are high. Variable resistor R607 sets the newburst level, and capacitor C607, inductor L607 and resistor R604 filterthe new burst envelope. U616 combines only the pre-pseudo sync, pseudosync, widened sync pulses and sums into inverting summing amplifier viaamplitude control R602 and R603. Summing amplifier A67 then has:pre-pseudo sync, widened H sync, new burst, and pseudo sync, and switchSW205 switches the output of amplifier A67 during the coincident times.

[0224]FIGS. 25a to 25 h show waveforms as labelled at various points inthe circuit of FIGS. 24a, 24 b.

[0225]FIG. 24C shows a typical PLL circuit for oscillator U65 of FIG.24a causing a varactor tuning diode LC oscillator 252 with a set-resetphase detector U70 and low pass filter (less than 1 KHz) includingresistor R700 and capacitor C700, and a D.C. amplifier 250 includingamplifier A70, and the associated components R702, C703, R703, R704 andvoltage reference V_(bb).

[0226] Another Method of Defeating Checker and Vertical Enhancements

[0227] Another circuit for defeating the checker and vertical pulses isshown in FIG. 26, where since switch SW100 is of low resistance,essentially the checker and vertical modification pulses are attenuatedand/or level shifted or replaced by a voltage that is the averagevoltage (due to switch averaging circuit 260) in the high-low states ofthe end of line (checker) pulses and the end of field (verticalmodification) pulses. For example, if the checker and verticalmodification pulses have high states of 30 IRE and low states of 0 IRE,the capacitor C1 will charge to a voltage to approximately$\frac{30{IRE–}\quad 0{IRE}}{2} = {15{{IRE}.}}$

[0228] Because switch SW100 is on during the checker period at the endof the line and on during the end of field pulses due to gate U304,during these times the capacitor C1 voltage overrides the input videosignal with approximately a 15 IRE level, enough to defeat the enhancedanti-copy signals.

[0229] In FIG. 26, enhanced anticopy video signals are fed to inputamplifier A1 which outputs into sync separator circuit 258 which outputsa short duration frame pulse (i.e. 10 μs) to reset memory addresscounters in circuit 260. Meanwhile, composite sync (including possiblypseudo sync pulses from the prior art basic anticopy process) is fed toa horizontal phaselock loop circuit (PLL) U303. The output of PLL U303is then a horizontal frequency pulse which starts about 2 μs before thefront porch of input video. The EPROM of circuit 260 has outputscorrelating to the checker and end of field pulses line locations in theTV field. One shot U100 outputs a pulse coincident with the checkerlocation within the horizontal line, while one-shots U200 and U300 forma pulse such that the output of U300 has a pulse coincident with the endof field pulses within the horizontal line. The locations of checker andend of field pulses are gated through gates U202 and U203 and “or'd” viagate U304 to output pulses coincident in time with checker (EOL) and endof field pulses of the input video. Switch SW103 turns on during thesecoincident times to attenuate via resistor RS and average out (viacapacitor C1) the enhanced copy protected signals, to output a moreviewable signal from amplifier A2.

[0230] Another defeat method is to switch in either or both peaknegative or peak positive clipper circuits during the presence of thechecker (EOL) and vertical modification (EOF) pulses, as shown in FIG.27. The input copy protected video is clamped by buffer amplifier A6.EOF and EOL locations are identified by the circuit and input to OR gateU305. Diode D1 positively clips the checker (high) gray pattern andvertical modification high gray pulses to render a more copiablerecording. Diode D2 negatively clips the (low) black level of both theEOL and EOF pulses to a gray level to render a copiable recording viaswitches SW101, SW102. Amplifier A7 buffers the actions of switchesSW101, SW102 to output a copiable video signal.

[0231] A third defeat method is to sense the checker pulses and verticalmodification pulses and add inverse pulses. Since the check pattern runsup or/and down, and the vertical modification pulses run up and down,the circuit of FIG. 28 senses and nulls out EOF and EOL pulses.

[0232] Although nulling may be less effective because reduces thechecker or end of field pulses to about blanking level (OIRE), nullingcan in some cases cause a more viewable picture. (Recall ideally thechecker and end of field pulses should be above about 20 IRE for totaldefeat). Nulling thus causes the Hi and Lo states of the checkers andend of field pulses to go to a low state (0 IRE). FIG. 28 shows anulling circuit. Video from amplifier A1 output of FIG. 26 is DCrestored to have blanking level about OV via components C15, D15, Vb15,R15 and A246 feed into switch SW124 that passes the checker and end offield pulses via “or” gate U247. Gate U247 has checker and end of fieldlocations “identified” via gates U202 and U203 from FIG. 26. InverterA82 inverts the signal from switch SW124 and sums in this invertedchecker/end of field pulse via resistor R2 back to incoming video (viaresistor R1) to null out the checker and end of field pulses. (ResistorsR1 and R1 have equal values). Amplifier A209 buffers this video signalwith nulled out checker and end of field pulses. (Resistor R6 keeps a DCbias to ground for inverting amplifier A82).

[0233] Yet another defeat method (for use against the EOL and EOFpulses) is to attenuate peak active video from 100% to 80% (by about20%), and also increase the sync amplitude (by about 50%) as shown inthe waveforms of FIGS. 29a and 29 b. This requires an increase ofcomposite sync from 40 IRE to about 60 IRE. This can also defeatpseudo-sync pulses of the kind disclosed in U.S. Pat. No. 4,631,603because the pseudo sync pulses therein are 40 IRE. With prolongedcomposite sync pulses, sync separation circuits tend to separate onlythe large sync pulses and ignore the smaller amplitude ones. Thus thepulse pairs (pseudo-sync plus AGC pulse) will not be sensed. FIG. 29ashows the original input waveform for one video line. FIG. 29b shows thevideo line waveform modified for both the checker and verticalmodification pulses.

[0234]FIG. 29b shows a resultant waveform with modified sync amplitudesto be about 50% over the standard video with checker and end of fieldpulses. Since the composite sync signals are larger, the attenuation bythe illegal copy will generally not be enough to cause the checker andend of field pulses to be of any effect when viewing an illegal copy.Because the horizontal and vertical sync are modified to be much larger,the TV or VCR sync separator will not mistrigger.

[0235]FIG. 30 shows a circuit to provide the waveform of FIG. 29b.Enhanced anticopy protected signals are input to an amplifier A84 withgain of 0.8. These input signals are also clamped and have blankinglevel equal to OV. Sync separator circuit 302 outputs composite sync CSto analog switch SW210 and 300 attenuator. Attenuator circuit 300attenuates the typical logic level of composite sync (i.e. 5V peak topeak) and via offset voltage—V. Attenuator circuit 300 outputs aregenerated composite sync of 60 IRE (with 0 IRE equal to OV) to −60 IRElevels. Switch SW210 then switches in this new regenerated sync tooutput via amplifier A505 a waveform like that of FIG. 29b.

[0236] Another defeat method as shown in the circuit of FIG. 31 is totrack and hold the active video line to replace the checker pulse withthe last value of active video before the beginning of the EOL pulses.

[0237] By using from the circuit of FIG. 26 A1 output and U202 outputalong with the circuit of FIG. 31, it is possible to defeat the checkersby tracking and holding. This method is similar to reinserting a knownvoltage during the time of checker pulses. Since most program materialis above 0 IRE (especially in NTSC where black level is 7.5 IRE),tracking and holding the video results in a level generally greater than7.5 IRE, which is enough to defeat the checkers when this level isre-inserted in the checker location.

[0238] Amplifier A90 receives input from amplifier A1 of FIG. 26.Amplifier A90 has a delay of 100 ns to 200 ns (via delay lines or lowpass filters) so that the pulse from gate U202 tracks and holds video100 ns to 200 ns just before the checker pulses. Switch 310 is on at alltimes and is off during the checker pulses' times. Thus, amplifier A92output essentially is video transparent until switch 300 turns off andcapacitor C107 fills in for 2 μs the last program pixel (greater thanapproximately 7.75 IRE) during the checker pulse time.

[0239] Another defeat method as shown in the waveforms of FIGS. 32a, 32b is to add a high frequency signal to the EOF and EOL pulses so as toeffectively level shift by the average DC level of the high frequencysignal. FIG. 32a shows in the upper waveform the video input signalincluding the EOF pulse, and in the lower waveform the high frequencylevel shifting signal having a frequency of 0.1 to 5 MHz. The lowerwaveform of FIG. 32a can be applied to the checker pulses as well (at afrequency of 3 MHz for example). The resulting VCR recorded signal isshown in FIG. 32b, with the wavy portion having a frequency 3 MHz. Theadded high frequency signal causes the VCR to respond only to theaverage DC level, thereby level shifting the high and low states of theEOF and/or EOL pulses so as to be ineffective.

[0240] Since these above described enhancements are dependent on the TVset circuitry as well, as shown in FIG. 33 these “anti-enhancement”(defeat) circuits 322 can be connected between a playback VCR 320 andthe TV 324 to ensure a more viewable image of the illegal tape copy,using if needed RF modulator 326.

[0241] Pre-sync Pulses Defeating Horizontal and Vertical Modifications

[0242] The following describes how wider than normal sync pulsereplacement (i.e. normal sync of 4.7 μs vs. wider sync of 6 μs to 10 μs)negates vertical modification (end of field) and checker (end of line)pulses respectively.

[0243] In the sync separators used in TV sets as shown in prior art FIG.10, the composite sync pulses charge up the input sync separatorcoupling capacitor C. The slice threshold is a function of the averagecharge time per TV line. The greater the charge time, the further the“slice” point is away from the blanking level. Also, because the slicepoint is ramping toward blanking level due to resistor R_(b) andcapacitor C, a sync pulse preceding the end of line pulses causes theramping to be temporarily slowed down as to avoid slicing during the endof line pulses or end of field pulses.

[0244]FIG. 34a shows the TV sync separator's response to a TV signal(inverted video representation) including the basic anticopy process ofU.S. Pat. No. 4,631,603 plus just the checker anti-copy enhancement. TheTV sync separator slice point 328 clearly falls into the “A” regions,(the checker regions) and thus causes on/off pre-sync pulses that resultin a checker pattern on the TV set picture.

[0245] The waveform of FIG. 34b shows the result of wider than normalsync pulses. The resulting TV sync separator slice point 330 clearlynever falls into the “A” checker region, and thus the TV does notexperience a checker pattern. The color burst waveform may need to beadded in the “CBX” region throughout the horizontal sync region toensure color lock of the TV or VCR.

[0246]FIGS. 35a, 35 b show respectively a normal video horizontal syncpulse and a widened horizontal sync pulse with regenerated color burst(CB) added to the second half of the widened sync pulse, and the colorburst added after the trailing edge of this widened horizontal syncpulse. The added regenerated color burst is to ensure that TV sets stillhave a color burst to lock onto, whether the TV triggers color burst offthe leading or trailing edge of sync.

[0247] The regenerated color burst is not necessary for the location ofthe vertical modification pulses sync; these happen at the bottom of theTV field which is generally not viewed.

[0248] The following explains how adding sync pulses and pre-sync pulsesnegates the effects of (defeats) the end of field and end of linepulses:

[0249] By adding sync and pre-sync pulses, the TV's sync separatorcoupling capacitor C charges up more. Thus the slice point of the syncseparator circuit moves away from blanking level, avoiding the end ofline pulses and end of field pulses.

[0250] The waveform of FIG. 34c shows video with added re-sync pulses;the TV or VCR sync separator slice point 331 does not go into the end ofline location. Similar results are shown for vertical modificationpulses with gating in pseudo sync pulses in FIG. 36c. FIG. 36a showsvertical modification pulse “B” with normal H sync width and TV syncseparator slice point 336. Note that the slice point 336 of the TV syncseparator slices into the vertical modification pulse B. FIG. 36b showsthe corresponding waveform with widened H sync width, having TV syncseparator slice point 338 that avoid slicing into the “B” region(vertical modification pulses).

[0251] Post-Sync Pulses Additional Horizontal Modifications

[0252]FIG. 37 shows a circuit to add post-pseudo sync pulses to enhanceanticopy effectiveness (i.e., further degrade viewability) when anillegal copy is made with the above described basic anticopy process ofU.S. Pat. No. 4,631,603.

[0253] Video with the basic anti-copy process plus other above-describedenhancements is input to resistor R9. Amplifier A1 buffers input videoand couples it via capacitor C1 into the sync separator U6. The verticalsync output of sync separator U6 resets a 12 bit counter U1. Counter U1is clocked by horizontal sync to a PLL U2 that is locked to compositesync. EPROM U3 selects on which lines the post-pseudo sync (PPS) mayappear. A pseudo-random distribution of post-pseudo sync may be used, asselected by EPROM U3. Signal D0 (an output of EPROM U3) inhibits oneshot OS3 accordingly. The burst gate signal from sync separator U6 isinverted and low pass filtered by capacitor C2 and resistor R2. VoltageVgen sums in a signal (i.e., 300 Hz triangle wave form) into capacitorC2. This causes a time varying threshold difference into one shot OS3and thus causes a position change. The output of one shot OS3 is a fixedpulse (i.e., 1.5 μs duration) with pulse position modulation for exampleof ±1 μs. The output of one shot OS3 blanks out any video to blankinglevel via switch SW1 and adds a pulse by variable R7 to generate a postpseudo-sync pulse. Summing amplifier A3 inverts the output pulse of oneshot OS3 to maintain the correct shape of the added post pseudo-syncpulse. FIGS. 38a to 38 e show waveforms at various points in the circuitof FIG. 37, as labelled. The amplitude of the post pseudo sync may beamplitude modulated via VGen2 and voltage controlled amplifier A41 whichis a multiplying amplifier. The output of amplifier A41 varies inamplitude according to VGen2, being OV when the post pseudo sync pulseis off.

[0254] Defeat Method and Apparatus for Post Sync Enhancement

[0255]FIG. 39a shows another defeat circuit for use with “video in”containing the above-described post pseudo-sync pulses (PPS) coupled tosync separator U1 by capacitor C1. That is, the circuit of FIG. 39areduces or removes the effect of the PPS pulses, rendering the videosignal recordable. Sync separator U1 feeds composite sync into ahorizontal phase lock loop U2. The H PLL U2 is phased to begin in thearea of the post pseudo sync pulse (after burst). One shot U5 triggersoff H PLL U2 to generate a pulse that contains the post pseudo-syncpulse. Vertical sync from one shot sync separator U1 triggers syncseparator U4 to generate a pulse from extending TV from line 4 to line21, and one shot U4 triggers one shot U5 to generate an active fieldpulse from lines 22 to 262. The output of one shot U5 (which is thecomplement of the vertical blanking interval) gates AND gate U10 so thatthe output of gate U10 is on only during the active TV field.

[0256] Thus the output of gate U10 indicates locations of the postpseudo-sync pulses during the active field. FIGS. 39b, 39 c, 39 d showwaveforms labelled for three points in the circuit of FIG. 39a.

[0257]FIG. 40a shows the output signal of gate U10 of FIG. 39a used todefeat the post pseudo-sync pulses by generating a pulse (PPSD)coincident to the PPS signal and level shifting via analog multiplier U6(part number 1494). Multiplier U6 increases or decreases the gain duringthe time the post pseudo-sync defeat pulse U10 output is present. Whensignal VID1 is provided to multiplier U6, the sync tip is OV at VID1. Byincreasing the gain at the right time, the result is waveform Z of FIG.40b. By using signal VID2 into multiplier U6 instead of VID1 and usingthe output of gate U10, multiplexer U6 is reconfigured to attenuate withthe positive going pulse of U10 output and the gain is reduced at theright time to produce waveform Y of FIG. 40c, defeating the process.

[0258] By using signal VID2 into an analog switch SW220 of the circuitof FIG. 40d, gate Ulo's output controls switch SW220 to insert areference voltage. If VR is OV, waveform X of FIG. 40e results in ablanked-out post pseudo-sync. If VR is at sync tip voltage (i.e., −40IRE), the result is waveform U of FIG. 40f which creates an additional Hsync pulse of fixed amplitude and position. This causes most TV sets tohave a static horizontal picture offset and none of the “waviness” thepost pseudo-sync pulse would otherwise cause.

[0259] By summing the output of gate U10 into amplifier A6 in thecircuit of FIG. 40g, level shifting occurs to defeat the postpseudo-sync pulse, the waveform for which is also shown in FIG. 40b.FIG. 40h identifies the position of the PPS and level shifting.

[0260] Finally, narrowing the post pseudo-sync pulse to defeat itseffect is done by slicing sync. As shown in FIG. 41a, amplifier A7receives video VID2 with a notched-out color subcarrier due to a notchfilter R100, inductor L100, and capacitor C100. Amplifier A7 outputslices both normal sync and post pseudo-sync by setting V_(bb2) toapproximately −10 IRE. By using AND gate U7, and the PPS from gate U10(FIG. 39a), gate U7 outputs a pulse that is inverted but identical tothe original post pseudo sync pulse at logic levels. One shot U8 istimed for greater than 90% of the pulse period of the post pseudo-syncpulse and then controls switch SW224 to truncate the leading edge of thepost pseudo-sync pulse by greater than 90%. The result is the waveformas seen in FIG. 41b “VIDEO OUT DD” which shows a very narrow postpseudo-sync pulse, so as to cause no response in any video device (i.e.,VCR or TV set). Also by summing the output of gate U7 (FIG. 41a) intoamplifier A6 of FIG. 40g via resistor R6, this results in an output thatis level shifted past pseudo sync, as seen in FIG. 40h. This method canpartially or fully cancel the post pseudo sync pulse amplitudes as well,which results in attenuated post pseudo sync.

[0261] Method and Apparatus for Reducing Effects of Basic AnticopyProcess Signals

[0262] The following describes a method and apparatus in which the basicanti-copy process signals consisting of pseudo sync and AGC (i.e. basicanticopy process) added pulses (as described above) are reduced ineffectiveness, without altering these added pulses. Unlike the abovedescribed previous methods for altering the added pulses via amplitudeattenuation, level shifting or pulse narrowing to offset the addedpulses' effect, the present method reduces the effects of added pulsesby further adding other pulses that counteract the gain reduction causedby the AGC and pseudo-sync pulses.

[0263] U.S. Pat. No. 4,631,603 describes how the AGC circuit in a VCRmeasures the incoming video signal amplitude using a sync and back porchsample. By adding extra sync pulses with a very high level back porch,gain reduction occurs. Because the AGC circuit in a VCR continuouslysamples the sync amplitude (via a sync sample and a back porch sample)the present method negates some of the anticopy signals by moving allthe back porch levels from blanking, to below blanking level (i.e. about−20 IRE units for NTSC video). It is also possible with the presentmethod to add extra pseudo-sync pulses in the area at the bottom of theTV field (end of field) where anticopy signals containing AGC andpseudo-sync pulses are not present. These “extra” pseudo-sync pulses arefollowed by pulses below blanking level.

[0264] Referring to FIG. 42a, the basic anti-copy protected video(“video in”) is coupled to a sync separator U2 (part number LM 1881 orequivalent). The composite sync from sync separator U2 triggers thetrailing edge of sync to a 3 μs one shot U3.

[0265] Vertical sync from sync separator U2 triggers one shots U4 and U5to form an active field pulse provided as an input to AND gate U1 which“ands” the active field pulse and the output of one-shot U3. The outputof gate U1 is then a 3 μs backporch pulse during the active TV field.(Alternatively, one-shots U4 and U5 are not necessary and one-shot U3output goes directly to resistor R6, eliminating U1, U4 and U5).Resistor R6 is a negative summing resistor that subtracts a level fromthe back porch of the video input. Input amplifier A0 buffers the videoinput and couples to capacitor C3, diode D1, resistor R3 and voltage Vbthat forms a sync tip DC restoration circuit. The output of feedbackamplifier A3 is supplied to resistor R7; this output has a lowered backporch. (See FIGS. 43a to 43 g showing signals at various locations inFIG. 42a, as labelled).

[0266] The circuit of FIG. 42b receives the video out 1 signal fromresistor R7 of the circuit of FIG. 42a and replaces the last 10 or 11lines of each TV field with TV lines containing pseudo sync pulsespaired with subsequent AGC pulses below blanking level, i.e. −10 IRE to−30 IRE. The video from the node of diode D1 of FIG. 42a contains videothat is DC restored to 0 volts for O IRE blanking level. Amplifier A2 ofFIG. 42b amplifies this video and couples it to horizontal lockoscillator U11 (using pin 1 of oscillator CA 31541, where the sync tipfrom amplifier A2 is at 7V). The output of oscillator U11 is a 32H phaselock loop and outputs a signal of about 503 KHz frequency. This 503 KHzoutput signal is amplified for logic levels by amplifier A2 and input tobinary divider U10.

[0267] Summing amplifier A4 outputs a square wave signal ofapproximately 2 μs on and 2 μs off of amplitude −20 IRE to −40 IRE.Voltage Vbb and resistor R9 set the proper DC offset voltage, whereasresistors R10 and R11 set the proper amplitude. In FIG. 42a one-shot U6generates an active line pulse of 32 μs duration from the beginning ofthe active horizontal line; one shots U7 and U8 are triggered by thevertical sync pulse to turn high during the last 11 lines of the activeTV field. AND gate U9 of FIG. 42b thus gates in a 4 μs period squarewave of levels of −20 IRE to −40 IRE during the last 11 horizontalactive lines of the TV field (where the pseudo sync and AGC pulses arenot generally located). Amplifier A5 and resistor R12 output a modifiedanticopy signal with lowered backporch pulses and new pseudo-sync andlowered negative AGC pulses.

[0268] The modified video signal provided by the circuit of FIGS. 42aand 42 b causes the AGC amplifier in a VCR to measure incorrectly. As aresult based on its measurements of the pseudo sync pulses (and withlowered back porch) paired with AGC pulses of reduced level, it appearsto the VCR that a low level video signal is present, and thus the VCRincreases the gain of its AGC amplifier. This offsets the reduction ofthe gain in the AGC VCR amplifier via the basic anticopy process. Theadded pseudo-sync pulses in the EOF locations each has in one embodimentat least about 2 μsec of blanking level (O IRE) following the trailingedge of each added pseudo-sync pulse to defeat the EOF (vertical )modification. This is accomplished by a switch or waveform replacementcircuit as described variously above. This is useful if the high stateof the EOF modification has an amplitude greater than 10 to 20 IPE. Inthe absence of the blanking level under these conditions, the EOFmodification effect may be reduced but the prior art basic anticopyprocess effect increased, thus increasing the EOL modification andpreventing defeat of the overall anticopy process.

[0269] The above description of the invention is illustrative and notlimiting; other modifications in accordance with the invention will beapparent to one of ordinary skill in the art in light of this disclosureand are intended to fall within the scope of the appended claims.

What is claimed is:
 1. A method of modifying a video signal subject tocopy protection to increase picture degradation where the copyprotection signal causes a reduced amplitude video signal to be recordedon the copy, comprising the steps of: blanking a portion of the videosignal at a location in the overscan portion of the video signal priorto a synchronization signal; and adding to the blanked location awaveform for indicating a video retrace prior to occurrence of thesynchronization signal.
 2. The method of claim 1 , wherein the step ofadding comprises adding the waveform only to portions of the videosignal having active video prior to the step at blanking.
 3. The methodof claim 1 , wherein the step of adding comprises adding the waveformduring an active video period and during at least a portion of ahorizontal blanking interval of selected lines of the video signal. 4.The method of claim 1 , wherein the waveform includes a negative-goingtransition located in the overscan portion of the video signal.
 5. Themethod of claim 4 , wherein the transition is at least down to the blacklevel of the video signal.
 6. The method of claim 4 wherein thetransition occurs on a plurality of consecutive lines of the videosignal, defining a black rectangle in the video signal as displayed,followed by a plurality of consecutive lines without such transitions, aplurality of such rectangles defining a pattern in one video field. 7.The method of claim 6 , further comprising the step of shifting thelocation of the transitions in successive lines, thereby causing thechecker pattern to shift vertically when viewed on a television monitor.8. The method of claim 7 , wherein the locations of the transitions areshifted at a frequency in the range of approximately three to five timesa field rate of the video signal.
 9. The method of claim 6 , wherein atleast some lines without such transitions each have a transition from anactive video level to a gray level, the transition being located priorto the horizontal synchronization signal in the line.
 10. The method ofclaim 1 , wherein the waveform is added to an overscan portion of thevideo signal.
 11. The method of claim 9 , further comprising the stepsof, in successive fields of the video signal, inverting the plurality ofblack rectangle instead be to the transition from an active video levelto a gray level, and inverting the lines having the transition from anactive video level to a gray level in a prior field to instead define ablack rectangle, the inversion occurring at a multiple of a field rateof the video signal.
 12. The method of claim 1 , wherein thesynchronization signal is a vertical synchronization signal, and thewaveform is of a type indicating a vertical retrace.
 13. The method ofclaim 1 , wherein the waveform is added to at least the last two linesof active video in a field of the copy protected video signal at thelower portion of the field, the waveform being of a type for causing thetelevision set to retrace vertically prior to recurrence of a verticalsync signal in the field.
 14. The method of claim 13 , furthercomprising the steps of changing a position of the waveform insuccessive video fields.
 15. The method of claim 14 , wherein theposition of the waveform is stepped by a predetermined number of linesin each successive field.
 16. The method of claim 13 , furthercomprising substituting the predetermined waveform for at least thefirst two lines of the vertical blanking interval.
 17. The method ofclaim 3 , wherein the waveform is inserted into at least two lineslocated at about the end of a field of the video signal.
 18. The methodof claim 1 , wherein the step of blanking comprises blanking only activevideo.
 19. The method of claim 1 , further comprising the steps of:generating a plurality of pulses having an amplitude extending below ablanking level of the video signal; and adding at least one of theplurality of generated pulses to selected active video lines of thevideo signal, each added pulse following the horizontal sync pulse andpreceding the beginning of an active video portion of one of theselected active video lines.
 20. The method of claim 19 , wherein theselected active video lines are chosen pseudo-randomly.
 21. A method ofmodifying a video signal subject to copy protection to increase picturedegradation when a copy of the copy protected video is played, where thecopy protection causes a reduced amplitude video signal to be recordedon the copy, comprising the steps of: providing a waveform of a type forindicating a video retrace; substituting the waveform in at least onehorizontal line of the video signal at a location prior to asynchronization signal in place of an active video signal otherwisepresent at that location, wherein the location is in an overscan portionof the video signal.
 22. A method of modifying a video signal subject tocopy protection to increase picture degradation where the copyprotection signal causes a reduced amplitude video signal to be recordedon the copy, comprising the steps of: providing a waveform of a type forindicating a video retrace; and substituting the waveform in at leastone horizontal line of the video signal at a location following asynchronization signal of the video signal.
 23. A method for enhancing avideo copy protection process which causes a reduced amplitude videosignal to be recorded on a copy of the video signal, the methodcomprising the steps of: inserting a pattern of alternating black andgray regions into an overscan portion of the active video portion of afield of the video signal; and in successive fields shifting thelocations of the rectangles, thereby causing a moving displacement inthe displayed video signal.
 24. A method of modifying a video signalsubject to copy protection to increase picture degradation when a copyof the copy protected video is played, where the copy protection causesa reduced amplitude video signal to be recorded on the copy, comprisingthe steps of: providing a waveform of a type for causing a televisionset on which the copy is being viewed to retrace horizontally prior tooccurrence of the horizontal sync signal; and substituting the waveformin at least one horizontal line of the video signal at a location priorto the horizontal sync signal in that line in place of an active videosignal otherwise present at that location.
 25. An apparatus formodifying a video signal subject to copy protection, to increase picturedegradation when a copy of the copy protected signal is played, wherethe copy protection causes a reduced amplitude video signal to berecorded on the copy, comprising: a blanker for blanking a portion ofthe active video of the video signal at a location prior to asynchronization signal in the overscan portion of the video signal; apulse generator for generating a predetermined waveform; and an adderfor adding the generated waveform to the blanked portion of the videosignal.
 26. The apparatus of claim 25 , wherein the blanker blanks atleast a portion of each of the last several lines of active video in aselected video field, and wherein the waveform is a video gray levelwaveform, and further wherein the adder operates to add in a successionof video fields, followed by a succession of video fields that thegenerated waveform is not added to.
 27. The apparatus of claim 26 ,wherein the blanker also blanks and the generated waveform is added toat least a portion of each of the first several lines of active video inthe vertical blanking interval immediately following the selected videofield.
 28. The device of claim 25 , wherein the blanker also blanks andthe generated waveform is added to at least a portion of the horizontalblanking interval of predetermined lines of the video signal.
 29. Theapparatus of claim 25 , wherein: the blanker blanks a portion of atleast one horizontal line of the copy protected video signal at alocation prior to the horizontal sync signal in that line and in theoverscan portion of the video signal; and the pulse generator generatesa waveform that is a negative-going transition down to at least theblack level of the video signal.
 30. The apparatus of claim 25 , whereinthe adder adds the generated waveforms into a plurality of consecutivelines of the video signal, thereby defining a black rectangle, followedby a plurality of consecutive lines with a gray level waveform inserted,a plurality of such black and gray rectangles defining a checker patternin a video field.
 31. An apparatus for modifying a video signal subjectto copy protection, to increase picture degradation when a copy of theprotected signal is played, where the copy protection causes a reducedamplitude video signal to be recorded on the copy, comprising: controlcircuitry for determining a portion of the active video of the videosignal at a location prior to a synchronization signal in an overscanportion of the video signal; a pulse generator for generating apredetermined waveform; and a switch for switching the predeterminedwaveform into the determined portion of the active video.
 32. A methodfor enhancing copy protection of a video signal having a plurality oflines in each field, there being a line synchronization pulse at thebeginning of each line and a field synchronization signal at thebeginning of each field, the video signal being subject to a protectionprocess which reduces the amplitude in a copy of the video signal,comprising the steps of: selecting at least some of the linesynchronization pulses in the video signal; and reducing a duration ofthe selected line synchronization pulses, thereby causing at least onespurious field synchronization pulse when a copy is made of the videosignal.
 33. The method of claim 32 , wherein the step of reducing thepulse duration comprises the steps of: generating pulses each having aduration less than that of each of the selected line synchronizationpulses, the generated pulses each being of opposite amplitude value andapproximately equal absolute amplitude to the selected linesynchronization pulses; and adding at least one of the generated pulsesinto the video signal at a location of one of the selected linesynchronization pulses, thereby effectively reducing a duration of eachof the selected line synchronization pulses.
 34. The method of claim 32, wherein the duration, after the step of reducing, of each of theselected line synchronization pulses is less than about 600 nsec. 35.The method of claim 32 , wherein the duration, after the step ofreducing, of each of the selected line synchronization pulses is suchthat a television set sync separator filters out the linesynchronization pulses and does not respond to the selected linesynchronization pulses.
 36. The method of claim 32 , wherein theduration after the step of reducing is approximately zero.
 37. Themethod of claim 32 , wherein the selected lines begin in about the tenthline and extend to near the end of each field of the video signal. 38.The method of claim 32 , further comprising the step of addingadditional line synchronization pulse into the video signal at linesnear the end of each video field while eliminating some of the originalsychronization signals.
 39. The method of claim 32 , wherein the step ofreducing comprises the steps of: generating pulses having a durationless than that of each of the selected line synchronization pulses, thegenerated pulses being of opposite amplitude value than the selectedline synchronization pulses; and adding at least one of the generatedpulses into the video signal at a location of one of the selected linesynchronization pulses, thereby effectively reducing a duration of eachof the selected line synchronization pulses.
 40. The method of claim 32, wherein the video signal includes a color burst following each linesynchronization pulse, and further comprising the step of extending aduration of the color burst in each selected line.
 41. The method ofclaim 32 , wherein the step of reducing comprises replacing the linesynchronization pulses with a reduced duration pulse.
 42. An apparatusfor narrowing line synchronization pulses in a video signal having linesynchronization pulses at the beginning of each line and a fieldsynchronization pulse at the beginning of each field, comprising: a syncseparator for providing indications of line and field synchronizationpulses in the video signal; line selector circuitry responsive to theprovided indications for selecting particular lines in each field of thevideo signal; a one-shot for generating a signal of predetermined lengthless than that of a line synchronization pulse in response to theprovided indications of the line synchronization pulses; and logiccircuitry for adding the generated signals to each of the selectedparticular lines at a location of the line synchronization pulse in eachselected line, thereby reducing a duration of the line synchronizationpulse in that line.
 43. A method of defeating copy protection pulsesadded to a video signal, the copy protection pulses being of a type tocause a video retrace at a time other than occurrence of a videosynchronization signal, and being located in an active video portion ofthe video signal, comprising the steps of: generating a signal having anamplitude about equal to an amplitude of the synchronization signal; andmodifying the video signal with the generated signa, wherein a deviationof the synchronization signal is thereby extended.
 44. A method ofdefeating copy protection pulses added to a video signal, the copyprotection pulses being of a type to cause a video retrace at a timeother than occurrence of a video synchronization signal, and beinglocated in an active video portion of the video signal, comprising thesteps of: generating a signal of a predetermined level; and adding thesignal to the video signal at said active video portion.
 45. The methodof claim 44 , wherein the predetermined level is at least about 20% ofpeak white of the video signal.
 46. The method of claim 44 , wherein thesynchronization signal is a horizontal synchronization signal.
 47. Themethod of claim 44 , wherein the synchronization signal is a verticalsynchronization signal.
 48. A method of defeating copy protection pulsesadded to a video signal, the copy protection pulses being of a type tocause a video retrace at a time other than occurrence of a videosynchronization signal, and being located in an active video portion ofthe video signal comprising the steps of: generating a signal of apredetermined level; and replacing the copy protection pulses with thegenerated signal.
 49. The method of claim 48 , wherein the predeterminedlevel is at least about 20% of peak white of the video signal.
 50. Themethod of claim 48 , wherein the synchronization signal is a horizontalsynchronization signal.
 51. The method of claim 50 , wherein thesynchronization signal is a vertical synchronization signal.
 52. Amethod of defeating a video copy protection scheme that reduces aduration of line synchronization pulses, thereby causing a spuriousfield synchronization pulse in the video signal when a recording is madethereof, comprising: determining a location of at least some of the linesynchronization pulses having reduced duration; and modifying the linesynchronization pulses to be of a longer duration.
 53. The method ofclaim 52 , wherein the longer duration is less than a duration of astandard line synchronization pulse.
 54. The method of claim 52 ,wherein the step of modifying comprises: generating a linesynchronization pulse; blanking the reduced duration linesynchronization pulse; and inserting the generated line synchronizationpulse in place of the blanked line synchronization pulse.
 55. The methodof claim 54 , wherein the generated line synchronization pulses are of aduration to extend into an adjacent active video portion of the line.56. An apparatus for defeat of anticopy pulses present in active videoportions of a video signal, the anticopy pulses being located at the endof at least some video fields and at the end of at least some videolines in the active video portions thereof, comprising: a sync levelrestoration circuit for restoring the horizontal sync pulse tips of thevideo signal to a predetermined level; circuitry for generating controlsignals of a first predetermined duration at the end of at least somelines of the video signal and of a second predetermined duration at theend of at least some fields of the video signal; and switch circuitrycontrolled by the control pulses for switching a particular signal levelinto the restored video signal, thereby permitting an acceptablerecording to be made thereof.
 57. The apparatus of claim 56 , whereinthe particular signal level is at least 20% of a peak white level of therestored video signal.
 58. An apparatus for defeat of anticopy pulsesadded to the active video portions of a video signal prior tosynchronization pulses, comprising: logic circuitry for generatingcontrol signals of predetermined duration during the active videoportions; and circuitry actuated by the control pulses for combining apredetermined signal into the active video portion, thereby permittingan acceptable recording to be made of the video signal.
 59. Theapparatus of claim 58 , wherein the logic circuitry generates thecontrol signals at times just prior to the occurrence of the horizontaland vertical blanking intervals of the video signal.
 60. The apparatusof claim 59 , wherein the predetermined signal is at least 20% of a peakwhite level of the video signal.
 61. The apparatus of claim 59 , furthercomprising a restoration circuit for restoring the video signal to apredetermined horizontal sync pulse tip level, the restored video signalbeing provided to the circuitry actuated by the control pulses.
 62. Theapparatus of claim 58 , wherein the circuitry actuated by the controlpulses includes at least one switch circuit.
 63. The apparatus of claim59 , wherein the circuitry actuated by the control pulses includes alevel shifting pulse signal generator.
 64. The apparatus of claim 59 ,wherein circuitry actuated by the control pulses replaces the activevideo portions for the predetermined duration with the predeterminedsignal.
 65. The apparatus of claim 58 , wherein the circuitry actuatedby the control pulses further generated horizontal blanking intervalpulses and replaces a horizontal blanking interval following at leastone of the active video portions with the generated horizontal blankinginterval pulses.
 66. The apparatus of claim 58 , wherein the circuitryactuated by the control pulses includes: at least one multipole switchfor combining the predetermined signal, wherein the multipole switch inone position passes a source video signal unchanged, and in a secondposition switches in the predetermined signal and switches out thesource video signal.
 67. An apparatus for defeat of an anticopymodification to a video signal, the anticopy modification includingreducing a duration of at least some of the horizontal synchronizationpulses in the video signal so as to be less than a standard duration,the apparatus comprising: logic circuitry for determining a location ofthe horizontal blanking interval in at least certain lines of the videosignal and generating a control signal in response; a pulse generatorfor generating a horizontal synchronization pulse of predeterminedduration; and switch circuitry for adding the generated horizontalsynchronization pulse to the video signal, the switch circuitry soadding in response to the control signal.
 68. The apparatus of claim 67, wherein the generated horizontal synchronization pulse is of lesserduration than the standard duration.
 69. The apparatus of claim 67 ,wherein the pulse generator also generates a color burst signal, and theswitch circuitry adds the generated color burst signal to the videosignal.
 70. An apparatus for defeat by level shifting of anticopy pulsespresent in the active video portions of a video signal, the anticopypulses being located at the end of at least some video lines in theactive portion thereof, comprising: a timing circuit for generating acontrol signal at a start of the anticopy pulses at the end of at leastsome video lines; a pulse generator for generating a pulse having aparticular level above a blanking level of the video signal at the endof each video line, in response to the control signal; and means foradding the generated pulse to the video signal, thereby increasing alevel of the end of each video line.
 71. The apparatus of claim 70 ,further comprising: a second timing circuit for generating a secondcontrol signal at the end of each video field; a second pulse generatorfor generating a second pulse having a particular level above a blankinglevel of the video signal in response to the second control signal; andmeans for adding the generated second pulse to the video signal, therebyincreasing a level of the end of each video field.
 72. The apparatus ofclaim 70 , further comprising: a generator for generating a horizontalsync pulse having a longer duration than a horizontal sync pulseotherwise present in the video signal; and a switch for replacing thehorizontal sync pulses otherwise present in the video signal with thegenerated horizontal sync pulses.
 73. The apparatus of claim 70 ,wherein the pulse generator includes a voltage controlled amplifier formultiplying a signal level of the video signal by a particular value.74. A method of defeating copy protection pulses added to a videosignal, the copy protection pulses being of a type to cause a videoretrace other than at occurrence of a video synchronization signal, andbeing located in an active video portion of the video signal, comprisingthe steps of: determining a location of the video synchronizationsignal; generating a pulse of an amplitude approximately that of thevideo synchronization signal; and adding the generated pulse to thevideo signal immediately prior to occurrence of the videosynchronization signal.
 75. The method of claim 74 , wherein the videosynchronization signal is a horizontal sync signal.
 76. The method ofclaim 74 , wherein the video synchronization signal is a vertical syncsignal.
 77. The method of claim 74 , wherein the added pulse incombination with the vertical sync signal is a serrated waveform. 78.The method of claim 75 , further comprising the step of adding a colorburst to the extended duration video synchronization signal.
 79. Amethod of defeating a video copy protection process, the process beingof a type to cause a video retrace at a time other than occurrence of avideo synchronization signal in a video signal and being located in anactive video portion of the video signal, and also including addedpulses extending below a blanking level of the video signal, the addedpulses being located in selected horizontal video lines of the videosignal between the horizontal sync pulse and about at the beginning ofactive video in each video line, the method comprising the steps of:generating a control signal at locations of the added pulses; andattenuating the added pulses in response to the control signals.
 80. Themethod of claim 79 , wherein the step of attenuating includes blankingthe added pulses.
 81. The method of claim 79 , wherein the step ofattenuating includes reducing a duration of the added pulses.
 82. Themethod of claim 79 , wherein the step of attenuating includes increasinga level of the added pulses relative to the blanking level.
 83. Themethod of claim 79 , wherein the step of attenuating includes reducingan amplitude of the added pulses.
 84. The method of claim 79 , whereinthe step of attenuating includes fixing the location of each of theadded pulses relative to the horizontal sync pulse in each horizontalvideo line.
 85. The method of claim 79 , wherein the step of attenuatingincludes the steps of: generating a high frequency signal; and addingthe generated high frequency signal to the video signal.
 86. A method ofdefeating a copy protection process that adds pulses to a video signal,the method comprising the steps of: reducing an amplitude of at least aportion of an active video part of the video signal; and increasing anamplitude of a synchronization pulse of the video signal.
 87. Anapparatus for defeating a video copy protection process, the processbeing of a type to cause a video retrace at a time other than occurrenceof a video synchronization signal in a video signal and being located inan active video portion of the video signal, and also including addedpulses extending below a blanking level of the video signal, the addedpulses being located in selected horizontal video lines of the videosignal between the horizontal sync pulse and the beginning of activevideo in each horizontal video line, the apparatus comprising: logiccircuitry for generating control signals at locations of the addedpulses; and an attenuator for attenuating the added pulses in responseto the control signals.
 88. The apparatus of claim 87 , wherein theattenuator includes a blanker for blanking the added pulses.
 89. Theapparatus of claim 87 , wherein the attenuator reduces a duration of theadded pulses.
 90. The apparatus of claim 87 , wherein the attenuatorincreases a level of the added pulses relative to the blanking level.91. The apparatus of claim 87 , wherein the attenuator reduces anamplitude of the added pulses.
 92. The apparatus of claim 87 , whereinthe attenuator fixes the location of each of the added pulses relativeto the horizontal sync pulse in each line.
 93. A method of defeating theeffects of a video anti-copy process that adds pulses to blankingintervals of a video signal, comprising replacing a back porch portionof the video signal having an amplitude at blanking level with a signalhaving an amplitude below the blanking level.
 94. The method of claim 93, wherein the amplitude below the blanking level is about −20 IRE units.95. The method of claim 93 , further comprising the steps of: generatinga plurality of negative-going pulses; and adding the plurality ofnegative-going pulses to about the last ten active lines of at leastsome fields of the video signal.
 96. The method of claim 95 , furthercomprising the step of modifying a portion of the video signal followingeach added negative-going pulse to be at a blanking level of the videosignal for a predetermined period.
 97. The method of claim 93 , whereinthe step of replacing includes adding a negative level shifting pulse tothe back porch portion of the video signal.
 98. A method of defeating avideo copy protection process that adds paired negative and positivegoing pulses to blanking intervals of a video signal, the method therebyenabling recording a viewable copy of the video signal, comprising thesteps of: determining a particular portion of at least some video linesof the video signal, the added pulses being present in the particularportion; and reducing a level of the particular portion to below ablanking level of the video signal.
 99. The method of claim 98 , whereinthe particular portion includes a backporch of each of the video lines.100. The method of claim 98 , wherein the level is lower than about −20IRE units.
 101. The method of claim 98 , further comprising the stepsof: determining a portion of each field of the video signal containingnone of the added pulses; generating a plurality of negative-goingpulses; generating a plurality of positive-going pulses having a levelof about −10 to −30 IRE; and adding the plurality of the generatednegative-going and positive-going pulses to the determined portion ofeach field.
 102. An apparatus for defeat of an anti-copy process thatadds paired negative-going and positive-going pulses to blankingintervals of a video signal, comprising: means for determining a backporch portion of the video signal, the back porch having an amplitude ofa blanking level of the video signal; and means for replacing the backporch portion with a signal having an amplitude below the blankinglevel.
 103. The apparatus of claim 102 , further comprising: a generatorfor generating a plurality of negative-going pulses; and means foradding the plurality of negative-going pulses to about the last tenlines of at least some fields of the video signal.
 104. An apparatus fordefeat of a video copy protection process that adds pulses to blankingintervals of a video signal, comprising: a generator for generating asignal below a blanking level of the video signal; timing circuitry fordetermining durations of particular portions of at least some lines ofthe video signal, the added pulses being present in the particularportions; and an adding circuit for adding the generated signal to thevideo signals at the determined duration.